Trojan:INCO.D/Boot is a boot sector trojan that targets the master boot record (MBR) or volume boot record (VBR) of infected systems, positioning itself to load before the operating system itself. This places it in an exceptionally privileged position, allowing it to hide from standard antivirus software and maintain persistent control over the compromised machine. Boot sector infections like this one are particularly dangerous because they survive operating system reinstalls and can be difficult for typical scanning tools to detect or remove.
While boot sector malware was more common in the era of physical media distribution, modern variants like Trojan:INCO.D/Boot still appear periodically, often bundled with other malware families or distributed through infected removable drives and compromised software installers. The "INCO.D" designation indicates this is part of a classified trojan family with documented variants, though specific behaviors can vary between samples.
Because this threat operates at the boot level, infected systems may exhibit unusual startup behavior, performance degradation, or security software failures. Standard removal procedures don't always work — the trojan loads before your antivirus does, giving it the upper hand. Professional removal may be necessary to fully clean the system without data loss.
Threat Profile
| Attribute | Details |
|---|---|
| Threat Family | Boot sector trojan (rootkit capabilities) |
| Detection Names | Trojan:INCO.D/Boot, Trojan.Boot.INCO.D, MBR:Trojan-INCO, VBR:Trojan.INCO (varies by vendor) |
| Platforms Affected | Windows systems (all versions with traditional BIOS/MBR; less effective on modern UEFI with Secure Boot enabled) |
| Discovery Period | Variants documented since mid-2010s; ongoing detection of related samples |
| Primary Distribution | Malicious USB drives, infected disk images, drive-by downloads, bundled with other malware installers |
| Persistence Mechanism | MBR/VBR infection — loads before Windows, survives OS reinstalls on the same disk without full wipe |
| Primary Capabilities | Rootkit functionality, security software evasion, payload delivery, possible keylogging, system manipulation at kernel level |
| Network Behavior | May connect to command-and-control servers; some variants download additional payloads; typical for this family to enable backdoor access |
| File System Artifacts | Minimal — primary infection resides in boot sector rather than traditional file system locations; may drop secondary components to disk |
| Registry Modifications | Varies — some variants modify low-level system settings; often bypasses registry entirely by operating at boot level |
| Removal Difficulty | High — requires specialized MBR repair tools or professional assistance; standard antivirus often cannot access infected boot sector while Windows is running |
| Data Theft Risk | Moderate to high — rootkit capabilities allow interception of credentials, keystrokes, and sensitive data before encryption |
How It Spreads
Boot sector trojans spread differently than typical file-based malware because they target the physical structure of your hard drive rather than the operating system itself. Trojan:INCO.D/Boot typically arrives on your system through infected removable media or as a secondary payload delivered by another piece of malware that's already compromised your machine. The infection process involves overwriting or modifying critical boot sector code, which means the original infection vector might not even be visible by the time you notice symptoms.
USB thumb drives remain a surprisingly common vector for boot sector infections. If you've ever plugged in a borrowed USB drive, picked up a seemingly blank drive from a conference, or used removable media from an untrusted source, you may have inadvertently given the malware an opportunity to infect your boot record. When an infected removable drive is inserted into a system configured to boot from USB (even if that boot attempt fails), some variants can still infect the hard drive's MBR during that brief connection window.
Other documented distribution methods include:
- Malware downloaders: Many modern infections begin with a file-based trojan that specifically downloads and installs a boot sector component to enhance persistence
- Compromised disk images and installation media: Pirated software ISOs, cracked game installers, or unofficial Windows installation media may contain boot sector modifications
- Exploit kits targeting vulnerabilities: Drive-by download attacks that exploit browser or plugin vulnerabilities to gain system-level access, then install boot sector components
- Infected system repair tools: Ironically, malicious "registry cleaners" or "system optimizers" from untrustworthy sources sometimes deliver boot sector malware while claiming to fix problems
- Network propagation from already-infected systems: In enterprise environments, lateral movement from one compromised machine to others on the same network
- Malicious firmware updates: Rare but documented cases where fake BIOS or firmware update utilities actually install boot-level malware
What It Does On Your Machine
Once installed, Trojan:INCO.D/Boot hijacks your computer's boot process by inserting itself between your BIOS and your operating system. When you power on your machine, the BIOS reads the master boot record from your hard drive and executes whatever code it finds there. In a clean system, that code simply loads Windows. In an infected system, the trojan's code runs first, loads itself into memory, and only then passes control to the legitimate Windows boot loader. This gives the malware complete control over everything that happens afterward — it's essentially already won before Windows even knows there's a fight.
The rootkit capabilities of this threat allow it to hide processes, files, network connections, and registry modifications from both the operating system and security software. Your antivirus might be running, but the trojan can intercept system calls and lie about what's actually on the disk or in memory. This makes detection extremely difficult using conventional scanning methods. Some variants implement keyloggers at such a low level that they capture keystrokes before encryption software or secure input methods can protect them, potentially compromising passwords, financial information, and other sensitive data you type.
Behavior typical of boot sector trojans in this family includes establishing backdoor access for remote attackers, downloading and executing additional malware payloads (ransomware, cryptocurrency miners, spyware), manipulating system security settings to disable protections, and potentially modifying or corrupting system files to maintain control. Network traffic may show suspicious outbound connections to command-and-control servers, though some variants use encrypted channels or proxy through legitimate services to avoid detection.
Performance impacts vary. Some infections cause noticeable slowdowns during startup as the malicious boot code executes, while others are carefully optimized to avoid detection through performance analysis. You might notice your antivirus disabled or failing to update, unusual disk activity when the system is supposedly idle, or strange error messages during boot. In some cases, the first obvious symptom is when security software from another vendor (run from a bootable USB) finally detects the infection that your installed antivirus couldn't see.
Manual Removal — Step by Step
Document your symptoms and back up critical data immediately
Before attempting any removal, make note of what behavior led you to suspect infection. If possible, boot from a clean USB drive (Windows installation media or Linux live USB) and back up any critical documents to external media. Do not copy executable files or the entire system — only irreplaceable documents and data. Boot sector malware rarely encrypts files, but removal procedures can sometimes fail and cause boot problems, so protecting your data is essential first step.
Create bootable rescue media from a known-clean computer
Download a reputable bootable antivirus rescue disk from a trusted vendor (Kaspersky Rescue Disk, Bitdefender Rescue CD, or similar) using a different, uninfected computer. Write this to a USB drive or burn to DVD. These specialized tools can scan and repair boot sectors because they load their own operating system and access your hard drive from outside Windows, where the rootkit cannot interfere with detection. Do not create this media on the infected machine — the malware may compromise the rescue disk itself.
Boot from the rescue media and run a full system scan
Configure your BIOS to boot from the USB drive or DVD you just created (usually accessed by pressing F2, F12, Del, or Esc during startup — the specific key appears briefly on screen). Once the rescue environment loads, run a complete scan of all drives. The tool should detect the boot sector infection and offer to repair or quarantine it. Allow the repair — this will restore your MBR to its clean state. This process typically takes 30 minutes to several hours depending on drive size and scan thoroughness.
Repair the Windows boot loader if necessary
After removing the boot sector infection, you may need to repair Windows' boot files if the malware corrupted them. Boot from Windows installation media (USB or DVD), select "Repair your computer," choose "Troubleshoot," then "Command Prompt." Run these commands: bootrec /fixmbr, then bootrec /fixboot, then bootrec /rebuildbcd. These commands restore the proper Windows boot loader. If you're not comfortable with command-line procedures, this is a good point to bring the machine to our shop.
Boot into Safe Mode with Networking and scan again
Once boot repairs are complete, restart and immediately press F8 (Windows 7) or Shift+F8 (Windows 8/10) to access Advanced Boot Options, then select Safe Mode with Networking. In Safe Mode, most rootkit components cannot load properly. Run Malwarebytes (free version is sufficient) and perform a thorough scan to catch any secondary payloads that may have been dropped to the file system. Boot sector trojans often install additional components as backup persistence mechanisms, so a clean boot sector doesn't necessarily mean a clean system.
Remove any detected threats and secondary infections
Quarantine everything the scanner finds. Pay special attention to items in your Startup folder, scheduled tasks, and any unknown drivers or services. If Malwarebytes or your rescue disk detected additional malware beyond the boot sector component, this confirms the infection was part of a larger compromise. Remove all detected threats before proceeding. Some variants drop backdoor tools or remote access trojans as secondary payloads, and those must be eliminated separately.
Check for BIOS-level infections (advanced threat variants)
While rare, some sophisticated malware families can infect BIOS firmware itself, surviving even complete hard drive wipes. Check your BIOS version against the manufacturer's website and update to the latest version if available. Most modern UEFI systems with Secure Boot enabled are protected against this attack vector, but if you're running older hardware or have Secure Boot disabled, a BIOS reflash using official manufacturer tools can eliminate this possibility. This step is optional for most home users dealing with common variants.
Change all passwords from a clean device
Because boot sector trojans often include keylogging capabilities that operate before operating system protections engage, assume any passwords typed since infection may be compromised. Using a different, trusted computer or mobile device, change passwords for email accounts, banking sites, social media, and any other sensitive services. Enable two-factor authentication wherever possible to protect against credential theft. Do not change passwords from the infected machine until you're confident the infection is completely removed and verified clean by multiple scans.
Reboot normally and verify system stability
Restart the computer and allow Windows to boot normally. Verify that startup time is normal, security software loads properly, and you can access the internet without interference. Run Windows Update to ensure all patches are current. Monitor system behavior for 24-48 hours watching for signs of re-infection: unexpected network activity, security software being disabled, or unusual startup delays. If problems persist, the infection may not be completely removed.
Consider professional data recovery if boot repair fails
If you cannot get Windows to boot properly after removal attempts, or if you encounter data loss during the repair process, stop and seek professional help. Boot sector infections can sometimes cause collateral damage to partition tables or file system structures, and aggressive DIY repair attempts can make recovery harder. Our shop has specialized forensic tools that can recover data even from systems with damaged boot structures and rebuild them properly. Don't risk your data by continuing to experiment if you're out of your depth.
Prevention
- Enable UEFI Secure Boot on compatible systems. Modern computers with UEFI firmware and Secure Boot capability can cryptographically verify boot components, blocking most boot sector malware from loading. Check your BIOS settings and enable this feature if your hardware supports it and you're running Windows 8 or later.
- Disable booting from USB and external devices in BIOS. Configure your boot order to prioritize only your internal hard drive and set a BIOS password to prevent unauthorized changes. This prevents accidental infections from malicious USB drives while still allowing you to manually override when you intentionally need to boot from external media.
- Never use untrusted removable media or borrowed USB drives. If you must use a USB drive from an unknown source, scan it with updated antivirus software on a non-critical machine before accessing the contents. Better yet, use online file transfer services instead of physical media whenever possible.
- Keep Windows and all security software current. Enable automatic updates for Windows, your antivirus, and all installed software. Many boot sector infections arrive as secondary payloads from other malware that initially exploited unpatched vulnerabilities in browsers, plugins, or system components.
- Maintain a reputable real-time antivirus solution. While boot sector malware can hide from running antivirus software once loaded, good security software can catch the initial infection vector before the boot sector is modified. Enable real-time protection and heuristic analysis features.
- Download software only from official sources. Avoid pirated software, key generators, and unofficial installers — these are common delivery mechanisms for all types of malware including boot sector trojans. Legitimate vendors digitally sign their installers, which Windows can verify.
- Create regular system image backups to external drives. Boot sector infections can be catastrophic if removal attempts damage your partition table. A recent system image lets you restore to a clean state. Keep the backup drive disconnected except during backup operations so it cannot be infected by malware on the main system.
- Be cautious with "system optimizer" and "registry cleaner" utilities. Many of these tools are themselves malware or unwanted programs. Windows doesn't need registry cleaning, and performance utilities from unknown vendors are frequent infection vectors. Stick with built-in Windows maintenance tools or well-established utilities from major vendors.
Bring It In
Boot sector infections are among the most technically challenging malware types to remove properly. They require specialized tools, sector-level hard drive access, and careful verification that both the infection and any damage it caused have been addressed. If you've read through the manual removal steps and feel uncertain about any of them — or if you've already tried removal and are still experiencing problems — don't risk your data by continuing to experiment. A failed removal attempt can sometimes make recovery more difficult or even impossible.
At Computer Repair Roswell, we handle boot sector malware regularly and have the specialized diagnostic tools necessary to detect and remove these infections safely. We can scan your drive at the sector level, repair or rebuild boot structures, recover your data if the infection caused corruption, and verify complete removal using multiple methods. Most boot sector malware removals take 2-4 hours in our shop, and we'll explain exactly what we found and what we did to fix it. Call us at the number above or stop by our Roswell location — we're here to help get you back to a clean, properly functioning system without the guesswork and risk of DIY attempts gone wrong.