Trojan:StartPage/ACP is a browser hijacker that forcibly modifies your web browser's start page, default search engine, and new tab behavior to redirect you through advertising networks or data-harvesting intermediaries. First documented in the mid-2010s, this threat family persists by altering both browser settings and Windows registry keys that control homepage behavior, making it frustratingly difficult to remove through normal browser reset procedures alone. While not as destructive as ransomware or banking trojans, StartPage/ACP demonstrates how persistent unwanted software can degrade your browsing experience, compromise your privacy, and serve as a gateway for additional malware installations.
This hijacker typically enters systems bundled with freeware installers, disguised as legitimate software updates, or hidden in the fine print of installation wizards that users click through without careful review. Once established, it generates revenue for its operators by forcing traffic through specific search portals and collecting browsing data—potentially including search queries, visited URLs, and even form data you enter on web pages.
Threat Profile
| Attribute | Details |
|---|---|
| Threat Family | Browser hijacker / StartPage redirector |
| Common Aliases | StartPage.ACP, Trojan.StartPage!gen, BrowserModifier:Win32/StartPage |
| Affected Platforms | Windows 7/8/8.1/10/11 (all editions); affects Chrome, Firefox, Edge, Internet Explorer |
| First Documented | 2014–2015 timeframe (family continuously updated) |
| Distribution Methods | Software bundling, fake updaters, malicious advertising, drive-by downloads |
| Persistence Mechanisms | Registry modification (HKCU\Software\Microsoft\Internet Explorer\Main, browser extension manifests), scheduled tasks, startup folder entries |
| Primary Capabilities | Homepage hijacking, search redirection, browser extension injection, user tracking, advertising injection |
| Typical File Locations | %LOCALAPPDATA%\[random]\, %APPDATA%\[vendor name]\, browser profile directories |
| Registry Artifacts | Modified Start Page values, SearchScopes alterations, browser helper objects, extension policy keys |
| Network Behavior | HTTP/HTTPS redirects through intermediary domains, tracking pixel requests, command-and-control check-ins (varies by variant) |
| Data at Risk | Browsing history, search queries, potentially form data and cookies |
| Removal Difficulty | Moderate—requires registry editing, browser cleanup, and detection of hidden persistence mechanisms |
How It Spreads
Trojan:StartPage/ACP rarely arrives as a standalone download. Instead, it piggybacks on software you actually wanted—free PDF converters, video codec packs, system optimizers, or screensavers from questionable download portals. The installation wizard presents a long End User License Agreement and pre-checked boxes buried several screens deep that authorize "modifying browser settings to enhance your experience." Most users click Next repeatedly without reading, unknowingly granting permission for the hijacker to install.
Fake update notifications represent another major vector. You might see a browser pop-up claiming "Your Flash Player is out of date" or "Critical Java update required," complete with official-looking logos. Clicking the update button downloads a bundled installer that includes StartPage/ACP alongside whatever legitimate software (if any) was promised. These fake updaters often appear on sketchy streaming sites, torrent portals, or compromised legitimate websites running malicious advertising.
The hijacker spreads through these common channels:
- Software bundlers: Download.com, Softonic, and similar third-party download sites that wrap legitimate freeware in installer packages containing additional "offers"
- Fake browser extensions: Chrome Web Store or Firefox Add-ons listings that promise ad blocking, coupon finding, or video downloading but actually install hijacking code
- Malicious email attachments: Invoice or delivery notification emails with .zip or .exe attachments that drop the hijacker as a secondary payload
- Compromised websites: Drive-by downloads exploiting outdated browser plugins (Flash, Java, Silverlight) to silently install without explicit user consent
- Social engineering: Pop-ups claiming your system is infected and offering a "free scan" that actually installs the hijacker
- Pirated software bundles: Cracked applications or game key generators that include browser hijackers as monetization for the illegal distribution
What It Does On Your Machine
Once installed, Trojan:StartPage/ACP immediately modifies several Windows registry keys that control browser behavior. In Internet Explorer and Edge, it changes the "Start Page" value in HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main to point to a controlled search portal or advertising landing page. For Chrome and Firefox, it deploys a browser extension or modifies preference files in the browser profile directory, overriding your configured homepage, new tab page, and default search engine.
The hijacked start page typically looks like a generic search engine—perhaps with a brand name like "SafeSearch," "QuickFind," or "BrowserAssistant." When you perform searches, results route through tracking intermediaries that log your queries before redirecting (sometimes) to legitimate search results from Google or Bing. The hijacker operators monetize this in two ways: selling your search behavior data to advertising networks, and earning referral fees when you click sponsored results that are injected into the results page.
Many variants of StartPage/ACP go further by injecting additional advertisements into websites you visit. You might see extra banner ads on pages that normally don't have them, pop-under windows that open behind your browser, or text on web pages that's been converted into hyperlinks (often double-underlined) leading to advertising landing pages. Some variants monitor for e-commerce sites like Amazon or eBay and inject fake coupon offers that actually redirect to competitor sites paying affiliate commissions.
Privacy implications extend beyond annoyance. The hijacker typically installs tracking cookies and may log every URL you visit, building a detailed profile of your interests, shopping habits, and online behavior. This data feeds targeted advertising networks—or worse, gets sold to data brokers who aggregate information from multiple sources. Some variants have been observed capturing form data, meaning passwords or credit card numbers entered on HTTPS sites could potentially be intercepted if the hijacker uses a man-in-the-middle proxy or keylogger component.
Manual Removal — Step by Step
Disconnect from the network
Unplug your Ethernet cable or disable Wi-Fi before proceeding. This prevents the hijacker from downloading additional components, communicating with command servers, or attempting to re-install itself from a remote source during the removal process.
Boot into Safe Mode with Networking
Restart your computer and repeatedly press F8 (Windows 7) or Shift+F8 (Windows 8/10/11) during boot. Select "Safe Mode with Networking" from the menu. In Windows 10/11, you can also go to Settings → Update & Security → Recovery → Advanced startup → Restart now, then choose Troubleshoot → Advanced options → Startup Settings → Restart → press 5 for Safe Mode with Networking. Safe Mode loads only essential drivers, preventing the hijacker's persistence mechanisms from running.
Identify and terminate suspicious processes
Open Task Manager (Ctrl+Shift+Esc) and look under the Processes tab for unfamiliar items with vague names like "BrowserHelper," "bhsvc," "svc_updater," or random character strings. Right-click any suspicious process, select "Open file location," note the path, then right-click again and choose "End task." The hijacker typically runs a background service to monitor and restore its settings.
Uninstall suspicious programs
Go to Control Panel → Programs → Programs and Features (or Settings → Apps on Windows 10/11). Sort by "Installed On" date and look for recently added programs you don't recognize—especially anything installed the same day your browser problems started. Common names include "Browser Assistant," "Search Protect," "Safe Finder," or generic entries like "Updater" with no publisher information. Uninstall anything suspicious, but be aware the hijacker's uninstaller often leaves components behind intentionally.
Remove persistence registry entries
Press Windows+R, type regedit, and press Enter. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and look for entries pointing to the file path you noted in step 3. Delete any suspicious Run entries. Also check HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and the corresponding RunOnce keys in both HKCU and HKLM. For Chrome enterprise policies, check HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome and delete the entire Chrome key if you find ExtensionInstallForcelist or similar policy entries.
Delete the hijacker's program folder
Navigate to the file location you identified in step 3 (typically in %LOCALAPPDATA% or %APPDATA%). Delete the entire parent folder. You may need to take ownership of the folder first—right-click the folder, choose Properties → Security tab → Advanced → Change owner to your account, check "Replace owner on subcontainers and objects," apply, then try deleting again. If Windows prevents deletion, use Shift+Delete to bypass the Recycle Bin.
Reset each affected browser
For Chrome: Settings → Reset settings → Restore settings to their original defaults. For Firefox: Help → More troubleshooting information → Refresh Firefox. For Edge: Settings → Reset settings → Restore settings to their default values. This removes hijacked extensions and restores default homepage/search settings. Note that reset will log you out of websites and clear some preferences, but bookmarks and passwords are preserved.
Run Malwarebytes or similar scanner
Download Malwarebytes Free (from malwarebytes.com—not a third-party download site) and run a full Threat Scan. Even if you've completed manual steps, a reputable scanner will catch remnants and related PUPs you might have missed. Quarantine or delete everything it finds. Consider also running a scan with HitmanPro or AdwCleaner for additional coverage of browser hijacker families.
Check scheduled tasks
Open Task Scheduler (search for it in the Start menu) and review the Task Scheduler Library. Look for tasks with suspicious names or that run executables from the paths you identified earlier. Right-click and delete any hijacker-related tasks. Some variants create tasks named to look legitimate (like "Google Update Service" pointing to a non-Google executable)—verify the Actions tab to confirm what actually runs.
Change your passwords
If the hijacker was active for more than a day or two, change passwords for critical accounts—email, banking, social media—from a known-clean device or after you've verified the infection is completely removed. Use a password manager going forward to avoid typing credentials that could be keystroke-logged. Enable two-factor authentication wherever possible as additional protection.
Reboot normally and verify
Restart your computer normally (not Safe Mode) and reconnect to the network. Open your browsers and verify that your chosen homepage loads, searches go to your preferred engine, and no unwanted extensions appear in the extensions list. Monitor for a day or two to ensure the hijacker doesn't reinstall itself from a persistence mechanism you missed.
Prevention
- Download software only from official sources. Avoid third-party download sites like Download.com, Softonic, or CNET Downloads. Go directly to the developer's website—if you want VLC, get it from videolan.org, not from a "free software portal" that wraps it in a bundler.
- Read every screen during installation. Don't click Next/Accept repeatedly. Look for checkboxes that offer to "change your homepage" or "install recommended software." Switch to "Custom" or "Advanced" installation mode instead of "Express" to see what's actually being proposed.
- Keep your browser and plugins updated. Enable automatic updates for Chrome, Firefox, or Edge. Remove obsolete plugins entirely—Flash, Java, and Silverlight are no longer necessary for modern web browsing and represent major security holes exploited by drive-by downloads.
- Use an ad blocker with anti-malvertising capabilities. uBlock Origin (not just "uBlock") blocks many malicious advertising networks that serve fake update notifications and hijacker installers. This provides defense-in-depth even if you accidentally click something suspicious.
- Maintain a reputable antivirus with real-time protection. Windows Defender (built into Windows 10/11) provides baseline protection and catches most browser hijackers. Consider supplementing with Malwarebytes Premium for additional behavioral detection of PUPs and hijackers that traditional antivirus sometimes misses.
- Don't trust email attachments or links from unknown senders. Even if an email looks like it's from UPS, Amazon, or your bank, verify through independent means (type the URL yourself, call the number on your credit card) before opening attachments or clicking links. Legitimate companies don't send invoices as .zip or .exe files.
- Create a standard user account for daily use. Don't browse the web or read email from an Administrator account. Standard users can't install software or modify system settings without explicitly entering an admin password, which blocks many automated hijacker installations.
- Back up regularly to external media. While browser hijackers don't destroy data like ransomware, a clean backup gives you the nuclear option—wipe and restore from known-good state—if an infection proves particularly stubborn. Store the backup drive disconnected from your computer to prevent it from being infected.
Bring It In
While the steps above work for technically confident users, browser hijacker removal can be frustrating. These threats deliberately hide components across multiple locations, and missing even one persistence mechanism means it'll reinstall itself the next time you reboot. If you've attempted removal and your homepage keeps resetting itself, or if you're simply not comfortable editing the Windows registry, bring your computer to our Roswell shop at 1365 Atlanta Street.
We typically resolve browser hijacker infections within a few hours—often same-day if you arrive in the morning. Our process includes not just removing the hijacker, but identifying how it got in and addressing those vulnerabilities (outdated software, risky browser extensions, security setting gaps) so you don't face the same problem next week. Call (770) 856-1578 to check current turnaround time, or just stop by Monday through Saturday. We're the local shop that's been keeping Roswell's computers clean for years, and we're here when you need straightforward help without the runaround.