Removal of the Extenbro trojan infection

What is Extenbro?

Extenbro is a trojan-type application designed to modify DNS system settings in the IPv4 protocol. Cyber criminals proliferate this malware using the "bundling" method, and thus Extenbro infiltrates computers during installation of other programs.

The main purpose of Extenbro is to protect adware-type infections and infiltrates computers together with the adware. To prevent users from eliminating these potentially unwanted applications (PUAs), Extenbro modifies DNS system settings, thereby blocking access to various cyber security websites with information regarding adware removal.

In addition, already installed anti-virus suites are no longer able to receive updates, and thus these programs will be unable to receive information about newly-released infections. In summary, Extenbro significantly increases the system's vulnerability to infection.

Extenbro creates a randomly-named folder in "%appdata%\Local" and also stores a randomly-named executable within this folder. This executable is then assigned as a scheduled task and is used to reassign DNS settings on each startup if changes performed by the user have been detected.

Therefore, as long as Extenbro is present, any DNS changes performed by the user will only be effective until the next system startup. Additionally, Extenbro uses Windows Registry Editor to add a root certificate and disable the IPv6 protocol - this is to ensure that the modified IPv4 protocol is used.

Extenbro also configures the Mozilla Firefox browser to use Windows Certificate Store by assigning Mozilla Firefox's "security.enterprise_roots.enabled" setting to "real". As mentioned, the purpose of Extenbro is to protect adware-type applications.

These malicious programs allow cyber criminals to generate revenue in malicious ways, such as redirecting users to dubious websites, displaying intrusive advertisements (pop-ups, banners, coupons, etc.), and gathering information (IP addresses, URLs visited, pages viewed, search queries, and similar) which can later be sold.

These applications significantly diminish the browsing experience and pose a serious threat to your privacy and computer safety, since delivered advertisements might redirect to malicious websites and collect information, which is sold to third parties (potentially, cyber criminals) who misuse it to generate revenue.

If you have recently noticed the presence of dubious applications, encounter unwanted browser redirects/intrusive advertisements, and the DNS settings have been changed, it is likely that your computer is infected with adware-type applications and a trojan such as Extenbro.

Therefore, immediately scan the entire system with a reputable anti-virus/anti-spyware suite and eliminate all detected threats, however, we strongly advise that you first manually revert DNS options (more information below) and update the installed anti-virus program. This will also allow you to download this software if it is not already installed.

The internet is full of adware-type applications, all of which share many similarities. By offering many "useful functions", these programs attempt to give the impression of legitimacy and trick users to install. In fact, they provide no real value for regular users, since their only purpose is to generate revenue for the developer.

Rather than enabling the functions promised, adware-type applications cause redirects, gather information, and deliver intrusive advertisements.

There are also many trojans online, most of which pose much greater threats than Extenbro. Trojan-type infections are typically designed to steal extremely sensitive data (account credentials, credit card details, etc.) and to inject other high-risk infections, such as ransomware, cryptominers, and so on.

How did Extenbro infiltrate my computer?

As mentioned above, Extenbro is "bundled" with various adware-type applications. "Bundling" is essentially stealth installation of third party applications together with regular software. Developers hide "bundled" programs behind "Custom/Advanced" settings (or other sections) of the download/installation processes.

Some high-risk applications such as Extenbro are hidden, and thus go unnoticed. Furthermore, many users often rush these procedures and skip steps. In doing so, they expose their systems to risk of various infections and compromise their privacy.

How to avoid installation of malware?

The main reasons for computer infections are poor knowledge of these threats and careless behavior. The key to safety is caution. Therefore, pay attention when browsing the Internet and downloading/installing software. Download programs from official sources only, preferably using direct download links.

Third party downloaders/installers often include rogue apps, and thus these tools should never be used. Bear in mind that PUAs are also distributed using intrusive advertisements, which typically seem legitimate. Once clicked, however, they redirect to dubious websites (gambling, adult dating, pornography, and similar).

If you experience these ads/redirects, eliminate all suspicious applications and browser plug-ins.

Have an Internet security suite installed and running at all times - these tools detect and eliminate malware before it harms the system. If you believe that your computer is already infected, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.

Screenshot of Extenbro process ("dpo231.exe") in Windows Task Manager:

IMPORTANT NOTE! As mentioned above, this trojan is designed to modify DNS settings, thereby preventing users from accessing cyber security websites and updating anti-virus suites. Therefore, to remove this malware, you must revert changes made by Extenbro:

1) Right-click on the "Start Button" and select "Network Connections":

2) Right-click on "Ethernet" and select "Properties":

3) Select "Internet Protocol Version 4 (TCP/IPv4)" and click "Properties":

4) Change the "Preferred DNS server" and "Alternate DNS server" entries to those recommended by your Internet service provider (you can typically find this information on the provider's official website) or to other legitimate DNS servers. We recommend using Google Public DNS, OpenDNS, or Cloudflare servers:

• Google Public DNS: 8.8.8.8 and 8.8.4.4
• OpenDNS: 208.67.222.222 and 208.67.220.220
• Cloudflare: 1.1.1.1 and 1.0.0.1

5) After changing the server settings, click the "Advanced" button, select the "DNS" tab, and remove all entries except those you have already entered:

After performing these steps, you will be able to access all chosen websites and download an anti-virus suite, or update your current version.

Bear in mind, however, that Extenbro trojan will reassign DNS settings after the next system startup and, therefore, you should not restart or shutdown your computer after performing these changes. You must first remove the threat, otherwise you will have to repeat these steps repeatedly.

How to remove malware manually?

Most trojan infections can be removed by running a full system scan with Combo Cleaner. The full manual procedure below is for cases where automatic removal failed, where you want to verify a scan caught everything, or where the threat has multiple persistence points.

Tools you'll need

Combo Cleaner Antivirus 7-days free trial

Recommended primary scanner. VB100 certified. The 7-day free trial is available.

Microsoft Defender Offline Free · built-in

Built into Windows. Boots to a clean environment to catch rootkits.

Process Explorer Free

From Microsoft Sysinternals. Better than Task Manager - shows full paths and signatures.

Autoruns Free

From Microsoft Sysinternals. Lists every place malware can persist on your system.

Microsoft Safety Scanner (MSERT) Free

Official Microsoft on-demand scanner. Always-current signatures - expires every 10 days.

Phase 1~ 5 min

Contain - limit the damage

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1

Disconnect from the network

30 secNo tool needed

Unplug your Ethernet cable and turn off Wi-Fi. If you're on a laptop, the airplane-mode key works fastest.

Why this matters

Many trojans exfiltrate data - saved browser passwords, banking sessions, screenshots - and accept remote commands. Cutting the network stops both immediately. Keep it disconnected until Phase 4.

2

Boot into Safe Mode with Networking

3 min

Safe Mode loads a minimal set of drivers and stops most malware from auto-running. "With Networking" lets you download tools - re-enable Wi-Fi only after you've booted in.

Windows 11

Open Settings → System → Recovery. Click Restart now next to Advanced startup.

Your computer will restart into the "Choose an option" menu. Click Troubleshoot → Advanced options → Startup Settings → Restart. After the second reboot, press 5 or F5.

Windows 10

Click the Windows logo, hold Shift, click the Power icon and choose Restart. In the Choose an option screen, click Troubleshoot → Advanced options → Startup Settings → Restart. Press F5.

Windows 8

Go to the Start Screen, type Advanced, select Settings → Advanced startup options → Restart now → Troubleshoot → Advanced options → Startup settings → Restart → F5.

Note: Windows 8 reached end-of-life in January 2023 - running on it puts you at much higher risk of reinfection.

Windows 7

Click Start → Shut Down → Restart → OK. As the system boots, press F8 repeatedly until the Windows Advanced Options menu appears, then choose Safe Mode with Networking.

Note: Windows 7 reached end-of-life in January 2020 - running on it puts you at much higher risk of reinfection.

Phase 2~ 15 min

Identify - find what's hiding

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3

Inspect running processes with Process Explorer

Tool: Process Explorer5 min

Download Process Explorer from Microsoft Sysinternals. Run it as Administrator. Click Options → Verify Image Signatures and View → Lower Pane View → DLLs.

Sort by "Verified Signer." Anything unsigned running from %AppData%, %LocalAppData%, %Temp%, or %ProgramData% is suspicious. Right-click → Properties to see the full image path. Right-click → "Search Online" to look up unfamiliar process names.

Why not just Task Manager

Task Manager hides full file paths, doesn't show digital signatures, and groups processes in ways that make malware easy to miss. Process Explorer is the same tool Microsoft engineers use.

4

Map every persistence point with Autoruns

Tool: Autoruns 14.x10 min

Download Autoruns. Right-click Autoruns.exe and choose Run as administrator - without elevation, Autoruns can't inspect protected registry hives.

In the menu, open Options → Hide Microsoft Entries and Options → Hide Empty Locations, then click Refresh.

Modern trojans don't just live in startup. Walk through these tabs and look for unsigned or unfamiliar entries:

• Logon - classic Run/RunOnce keys
• Scheduled Tasks - frequent hiding spot, especially tasks with PowerShell, MSHTA, or rundll32 actions
• Services - unsigned services in non-Microsoft folders
• WMI - Event Subscriptions are a stealthy persistence mechanism (MITRE T1546.003)
• Image Hijacks - Image File Execution Options "Debugger" abuse
• AppInit - DLLs loaded into every GUI process
• Browser plug-ins - unsigned add-ons across all installed browsers

Pro tip

Right-click any suspicious entry → "Jump to Image" to see the actual file. Right-click → "Search Online" opens VirusTotal for the file hash. Don't delete yet - just write down the file paths and entry names. We'll remove them after the scans.

5

Check the hosts file and DNS settings

3 minBuilt into Windows

Trojans often redirect bank, antivirus, and update domains to attacker-controlled servers by editing the hosts file or DNS settings.

Hosts file: Open Notepad as Administrator and open C:\Windows\System32\drivers\etc\hosts. Legitimate entries are commented with #. Any uncommented IP-to-domain mapping is suspicious - especially redirects for microsoft.com, windowsupdate, or your bank.

DNS settings: Open Command Prompt as Administrator and run ipconfig /all. Confirm your DNS servers point to your ISP, your router, or a known public resolver (Cloudflare 1.1.1.1, Google 8.8.8.8). Then open Settings → Network & internet → [your adapter] → DNS server assignment and verify both DNS and DNS over HTTPS (DoH) settings haven't been hijacked.

Why this matters

A clean PC with hijacked DNS is still a compromised PC. You'll think you're at chase.com and you'll be at the attacker's clone.

Phase 3~ 60-90 min

Remove - three scans, one cleanup

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No single antivirus catches everything. The order below is intentional: offline scan first (catches rootkits before Windows fully loads), then on-demand scanners on the running system, then manual cleanup of anything they missed.

6

Run Microsoft Defender Offline

Tool: Built into Windows15 min

Reboot to normal Windows. Open Windows Security → Virus & threat protection → Scan options. Select Microsoft Defender Antivirus (offline scan) and click Scan now. Your computer will restart into a stripped-down environment and scan before the full operating system loads.

Why this comes first

Rootkits and bootkits hide from any scanner running on the same Windows session that's already infected. A pre-boot offline scan sees the disk before the malware can hide itself.

Recommended antivirus

Combo Cleaner

VB100 certified. Includes anti-trojan, registry/persistence scanning, anti-spyware in one pass. The 7-day free trial is available.

Download Combo Cleaner

7

Run Combo Cleaner full system scan

Tool: Combo Cleaner20-40 min

Install Combo Cleaner and run a full system scan (not the quick scan). Let it complete fully, review the detected threats, and apply the recommended actions. Combo Cleaner will quarantine known trojans and registry persistence.

8

Run Microsoft Safety Scanner as a second-opinion scan

Tool: Microsoft Safety Scanner15 min

Download Microsoft Safety Scanner (MSERT.exe), Microsoft's free on-demand tool. The binary expires every 10 days, which means every download has the latest signatures. Run a full scan after Combo Cleaner to catch anything one engine alone might miss.

Why a second scan

Different scanning engines catch different threats. Running an additional Microsoft scan after Combo Cleaner is the single most underused verification step in malware removal.

9

Manually remove anything still listed in Autoruns

Tool: Autoruns10 min

Reopen Autoruns. Anything you flagged in Step 4 that's still present hasn't been caught by the automated scans. For each remaining suspicious entry: right-click → Delete in Autoruns (this removes the persistence registration), then navigate to the file path and delete the actual file. Empty the Recycle Bin.

Important

Some malware files reappear after deletion because something else on the system recreates them. If you delete a file and it returns within minutes, you have a remaining persistence point that Autoruns didn't show - usually a service or scheduled task running under SYSTEM. Re-run the scans from Steps 6-8 or proceed to a clean install (see end of guide).

Phase 4~ 15 min

Recover - restore browsers and security

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10

Reset browsers and clear notification permissions

5 min

Trojans and adware frequently hijack browsers - change the default search engine, install rogue extensions, or grant themselves notification permissions to keep displaying scam pop-ups even after the malware is gone.

• Chrome: visit chrome://settings/reset and click "Restore settings to their original defaults." Then visit chrome://settings/content/notifications and remove any unfamiliar sites.
• Edge: visit edge://settings/reset. Then check edge://settings/content/notifications.
• Firefox: open about:support and click Refresh Firefox (Firefox uses "Refresh," not "Reset"). Then check Settings → Privacy & Security → Permissions → Notifications.

Review installed extensions in each browser and remove anything you don't recognize, especially extensions you didn't install yourself.

11

Re-enable Defender, Tamper Protection, and update everything

10 min

Many trojans disable security software. Open Windows Security → Virus & threat protection → Manage settings and confirm Real-time protection, Cloud-delivered protection, and Tamper Protection are all turned on. Tamper Protection prevents malware from disabling Defender silently.

Then run Windows Update (Settings → Windows Update → Check for updates) and update your browsers and applications. The infection vector that let the trojan in originally usually involves outdated software.

Phase 5~ 15 min + 7 days

Verify & secure

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12

Change passwords from a clean device

20 min⚠ Critical

If the trojan was an info-stealer (Lumma, RedLine, Vidar, and similar are extremely common), assume every password saved in your browser is compromised. Change them from a different, known-clean device - your phone is fine if it's not infected.

Recommended order:

1. Primary email first - it's the recovery hub for everything else
2. Banking and financial accounts
3. Password manager master password (if you use one)
4. Social media, shopping, and remaining accounts

Where available, enable phishing-resistant multi-factor authentication (passkeys / FIDO2 hardware keys / authenticator apps) - SMS-based MFA is bypassable by sophisticated attackers.

13

Verify the clean and monitor for 7 days

5 min + 1 week monitoring

Reconnect to the network and run one final full scan with Combo Cleaner. Open Task Manager (Ctrl + Shift + Esc) and switch to the Startup apps tab - confirm nothing suspicious has reappeared.

Over the next 7 days, watch for symptom recurrence: unexpected high CPU usage, unknown processes returning, browser redirects, or pop-ups. If anything returns, you missed a persistence point and the procedure needs to be repeated - or you may have a deeper compromise that requires a clean install.

When to clean install Windows instead

Manual removal isn't always the right answer. Reinstalling Windows from scratch is the only way to be 100% certain when:

• The malware reappears after every removal attempt
• A bootkit or UEFI rootkit was detected (this class of threat sits below the operating system and survives a normal Windows reinstall)
• A confirmed credential-theft trojan ran with administrator privileges (Lumma, RedLine, Vidar) - the system likely has multiple unknown payloads
• The PC is used for online banking, business email, or anything where partial doubt isn't acceptable

A clean install is a 30-60 minute process: Windows 11 reinstall via Settings → System → Recovery → Reset this PC → Remove everything → Cloud download. Back up documents to external storage first, scan the backup with Combo Cleaner before restoring it, and reinstall applications fresh - never restore them from a backup of the infected system.

Important: Manual removal requires advanced computer skills. If you're not confident identifying system files from malicious files, run an automated scan with Combo Cleaner and Windows Defender and stop there - that path catches the vast majority of consumer trojans without the risk of breaking Windows by deleting the wrong file.