FileCoder.DAI is a file-encrypting ransomware variant that locks victims' documents, photos, and other personal files using strong cryptographic algorithms. Once executed, this threat systematically encrypts files across local and network-accessible drives, appending a distinct extension to affected filenames and dropping ransom notes demanding payment in cryptocurrency for the decryption key. Like most modern ransomware families, FileCoder.DAI renders files completely inaccessible without the attacker's cooperation, making it one of the more serious threats a computer owner can face.
This ransomware variant emerged as part of the broader FileCoder family, which has spawned numerous variants targeting Windows systems worldwide. Victims typically discover the infection only after the encryption process completes, when they find their family photos, tax records, business documents, and other irreplaceable files renamed and unusable. Understanding how this threat operates and how to prevent it is essential for anyone storing important data on their computer.
Threat Profile
| Attribute | Details |
|---|---|
| Family | FileCoder ransomware family |
| Aliases | Ransom:Win32/FileCoder.DAI, Trojan-Ransom.Win32.FileCoder, DAI Ransomware |
| Platform | Windows (all modern versions) |
| Discovered | Variant activity documented 2017–2019 |
| Encryption Algorithm | Typically AES-256 with RSA-2048 key protection (common for this family) |
| File Extension Added | Varies by variant (.locked, .encrypted, or custom extensions) |
| Distribution Methods | Malicious email attachments, exploit kits, software cracks, compromised RDP connections |
| Ransom Note Filename | Typically README.txt, HOW_TO_DECRYPT.html, or similar (varies) |
| Persistence Mechanism | Registry Run keys, scheduled tasks (varies by variant) |
| Network Behavior | Contacts command-and-control server for key exchange; may scan for network shares to encrypt |
| Data Exfiltration | Not typically associated with this family (pure encryption focus) |
| Removal Difficulty | Moderate (removing the malware itself); file recovery ranges from difficult to impossible without backups |
How It Spreads
FileCoder.DAI primarily spreads through social engineering tactics that trick users into executing the malicious payload. The most common delivery mechanism involves phishing emails disguised as legitimate business correspondence—invoices, shipping notifications, payment confirmations, or urgent messages from financial institutions. These emails contain attachments (often disguised as PDFs or Word documents) or links to download sites hosting the ransomware executable. When a user opens the attachment or downloads the file, the infection process begins immediately.
The ransomware also spreads through compromised software distribution channels. Victims searching for free versions of paid software, game cracks, or pirated activation tools frequently download bundles that include FileCoder.DAI alongside the desired program. Torrent sites, file-sharing networks, and dubious download portals serve as convenient distribution points for attackers who bundle ransomware with popular software titles.
Additional infection vectors include:
- Malvertising campaigns — Compromised or malicious advertisements on legitimate websites that trigger drive-by downloads when clicked
- Exploit kits — Automated attack tools that scan for vulnerabilities in browsers, Flash, Java, and other plugins to silently install ransomware
- RDP brute-force attacks — Attackers scanning for exposed Remote Desktop Protocol connections with weak passwords, then manually deploying ransomware after gaining access
- Infected USB drives — Less common but still observed, particularly in environments where users frequently share portable storage devices
- Software update imposters — Fake security alerts claiming your Flash Player, browser, or codec needs updating
- Compromised websites — Legitimate sites hacked to serve malware through watering hole attacks targeting specific visitor demographics
What It Does On Your Machine
Once executed, FileCoder.DAI operates with methodical efficiency. The ransomware typically begins by copying itself to a location within the user's profile directory, often using a random filename to avoid easy detection. It then establishes persistence mechanisms to ensure it survives system restarts, though the encryption process usually completes before a user has opportunity to reboot. The malware may attempt to communicate with its command-and-control server to register the infection, receive encryption keys, or transmit system information about the victim.
The core functionality focuses on file encryption. FileCoder.DAI scans all accessible drives—local hard drives, external USB storage, mapped network drives, and sometimes cloud storage folders that sync to the local system. It targets hundreds of file extensions associated with user-created content: documents (DOC, DOCX, PDF, XLS, XLSX), photos (JPG, PNG, RAW, PSD), databases (SQL, MDB, DB), archives (ZIP, RAR), videos, and more. The ransomware typically avoids encrypting system files necessary for Windows to boot, as attackers want victims able to access their computers to see the ransom demand and make payment.
During encryption, the ransomware uses strong cryptographic algorithms that make file recovery without the decryption key mathematically impractical. After encrypting each file, FileCoder.DAI renames it by appending a new extension, making the damage immediately visible when users browse their folders. Upon completing the encryption process, the malware drops ransom notes in multiple locations—typically on the desktop, in the Documents folder, and in every directory containing encrypted files. These notes provide instructions for payment, usually demanding Bitcoin or another cryptocurrency sent to a specific wallet address, with threats that the decryption key will be destroyed if payment isn't received within a specified timeframe.
Some variants of FileCoder.DAI also attempt to delete Windows Shadow Volume Copies, which are the system's automatic backup snapshots. By executing commands like vssadmin delete shadows /all /quiet, the ransomware eliminates one of the most accessible recovery options for victims. This deliberate sabotage of built-in recovery mechanisms demonstrates the sophisticated understanding modern ransomware authors have of Windows operating system features.
Manual Removal — Step by Step
Isolate the Infected Machine
Immediately disconnect the computer from all networks by unplugging the Ethernet cable and disabling Wi-Fi. Disconnect any external drives, USB devices, or network-attached storage to prevent the ransomware from encrypting additional files if the process is still ongoing. If you're on a business network, notify your IT administrator immediately. The faster you isolate the infection, the less damage it can cause.
Enter Safe Mode with Networking
Restart the computer and enter Safe Mode, which loads Windows with only essential drivers and services. This prevents most malware from executing automatically. To access Safe Mode, restart your PC and repeatedly press F8 (or Shift+F8 on newer systems) during boot. Select "Safe Mode with Networking" from the menu. On Windows 10/11, you may need to hold Shift while clicking Restart from the Start menu, then navigate to Troubleshoot > Advanced Options > Startup Settings > Restart > press 4 or F4 for Safe Mode with Networking.
Identify and Terminate Malicious Processes
Open Task Manager (Ctrl+Shift+Esc) and look for suspicious processes—unfamiliar names, processes running from temporary directories, or executables with random character strings. In Safe Mode, FileCoder.DAI may not be actively running, but check anyway. Look for processes located in %APPDATA%, %TEMP%, or %LOCALAPPDATA% folders. Note the full path of any suspicious process before terminating it, as you'll need to delete these files in subsequent steps.
Remove Persistence Mechanisms
Press Windows+R, type "regedit", and press Enter to open Registry Editor. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run. Look for entries with unfamiliar names or paths pointing to random folders in your user profile. Delete any suspicious entries. Also check Task Scheduler (type "taskschd.msc" in Windows+R) for scheduled tasks with random names or those pointing to suspicious executable locations. Right-click and delete any malicious tasks.
Delete the Malware Files
Using File Explorer, navigate to the locations you identified in Step 3. Common locations include folders within %APPDATA%\Microsoft\Windows\ with GUID-style names, %LOCALAPPDATA%\Temp\, and random folders in your user profile. Delete the entire folder containing the malicious executable. Also delete any ransom notes (README.txt, HOW_TO_DECRYPT.html, etc.) from your Desktop and other locations. Enable "Show hidden files" in File Explorer's View options to ensure you can see all folders.
Run Comprehensive Anti-Malware Scans
Download and install Malwarebytes (the free version works fine for cleanup) from a clean computer if necessary, transferring it via USB drive. Run a full system scan in Safe Mode with Networking. Also run a scan with your existing antivirus if it's from a reputable provider (Microsoft Defender, Norton, Kaspersky, Bitdefender, etc.). These tools may catch residual components, related malware, or additional threats that arrived with the ransomware. Quarantine or delete all detected items.
Check for Free Decryption Tools
Before despairing over encrypted files, check No More Ransom Project (nomoreransom.org) and security vendors like Emsisoft, Kaspersky, and Avast for free decryption tools. While FileCoder.DAI variants may not have public decryptors available, new tools are released regularly as researchers crack older ransomware families. Upload one encrypted file and its original (if available) to ID Ransomware to identify your specific variant, which will indicate if decryption is possible.
Restore from Backup
If you maintain regular backups to an external drive that wasn't connected during the infection, or cloud backups with version history, this is the time to use them. Before connecting backup drives, ensure you've completed all previous removal steps and verified through scans that the system is clean. Restore your files from the most recent clean backup. If you don't have backups, professional data recovery services may have limited options, but success rates for ransomware encryption are typically low.
Reset Passwords and Enable Two-Factor Authentication
From a clean computer or after thorough system verification, change passwords for all important accounts—especially email, banking, and any services where payment information is stored. Although FileCoder.DAI focuses on encryption rather than data theft, ransomware infections sometimes arrive with information-stealing trojans as companions. Enable two-factor authentication on all accounts that support it to add an additional security layer beyond just passwords.
Reboot and Monitor
Restart the computer normally (not in Safe Mode) and monitor system behavior carefully. Watch for unusual processes in Task Manager, unexpected network activity, or system slowdowns. Check that startup programs are limited to legitimate applications. Run another quick scan with Malwarebytes and your antivirus after 24 hours to ensure nothing reactivated. If problems persist or you're uncertain the threat is completely removed, professional assistance is recommended.
Prevention
- Maintain offline backups religiously. Follow the 3-2-1 rule: three copies of your data, on two different media types, with one copy stored offsite or offline. Disconnect external backup drives immediately after backing up, so ransomware can't encrypt them. Cloud backups with file versioning provide additional protection if configured to retain multiple historical versions.
- Keep Windows and all software updated. Enable automatic updates for Windows, and regularly update browsers, PDF readers, Java, Flash (or better yet, uninstall Flash), and all other applications. Many ransomware infections exploit known vulnerabilities that patches have already fixed. Security updates exist for a reason—install them promptly.
- Exercise extreme caution with email attachments. Never open attachments from unknown senders. Verify unexpected attachments even from known contacts by calling them directly—not replying to the email—since accounts get compromised. Be particularly suspicious of ZIP files, executables, Office documents with macros, and files with double extensions like "invoice.pdf.exe".
- Use reputable security software. Install antivirus/anti-malware from established vendors and keep it updated. Enable real-time protection. While no security software catches everything, quality protection blocks the vast majority of common threats. Microsoft Defender (built into Windows 10/11) provides solid baseline protection if kept updated.
- Disable macros in Office documents. Configure Microsoft Office to disable macros by default, allowing them only in trusted documents from verified sources. Many ransomware variants spread through Word and Excel files that use malicious macros to download and execute the payload. Legitimate documents rarely require macro functionality.
- Implement the principle of least privilege. Don't use an administrator account for daily activities. Create a standard user account for web browsing, email, and routine tasks. Ransomware running under a limited account has restricted system access and can't easily install persistence mechanisms or encrypt system-level protected files.
- Disable Remote Desktop Protocol if not needed. If you must use RDP, secure it with strong passwords, change the default port, implement account lockout policies, and use a VPN for remote access. Public-facing RDP connections are prime targets for ransomware gangs who use automated tools to brute-force credentials.
- Be skeptical of software from unofficial sources. Download programs only from official vendor websites or trusted platforms like the Microsoft Store. Avoid torrent sites, crack download pages, and file-sharing networks. "Free" versions of paid software often come bundled with ransomware, trojans, and other malware that costs far more than the legitimate software license.
When Computer Repair Roswell professionally removes malware from your system, we back our work with a 90-day warranty. If the same infection returns within 90 days due to residual components we missed, we'll re-clean your system at no additional charge. Our technicians use professional-grade tools and techniques that go beyond consumer antivirus software, ensuring thorough removal and system hardening against reinfection.
Bring It In
Ransomware removal and recovery isn't a job for generic online tutorials or automated fix-it tools. Every infection has unique characteristics, and encrypted files represent a crisis that demands immediate expert attention. The professionals at Computer Repair Roswell have handled hundreds of ransomware cases, and we understand the urgency when your family photos, business records, or critical documents are locked and inaccessible. We'll assess whether decryption tools exist for your specific variant, recover files from shadow copies if available, thoroughly clean all malware components from your system, and help you implement backup strategies to prevent future disasters.
Don't waste precious time downloading questionable removal tools or risk making the situation worse through trial-and-error. Call us at (770) 966-9889 or bring your infected computer to our Roswell location immediately. We're located in the heart of Roswell, easily accessible from Alpharetta, Sandy Springs, and surrounding North Atlanta communities. Our technicians will provide straight talk about your recovery options, transparent pricing, and professional service backed by our 90-day warranty. When your data is on the line, you need experienced professionals who've seen every ransomware variant and know exactly how to respond. That's what we do, every day, right here in Roswell.