Remove Trojan:Win32/Sirefef.AC

Threat Summary

Threat: Trojan:Win32/Sirefef.AC
Type: Trojan
Brief Description: This threat belongs to a family of Trojan that modifies browser's home page and search area.
Alias: TROJ_ZACCESS.CQJ, Trojan.Sirefef.BV, Troj/ZAccess-AH, Trojan horse Crypt.AQLW, TR/Sirefef.BV.2, ZeroAccess, Trojan.Zeroaccess!inf
Removal Tool: ▼ DOWNLOAD MalwareFox


Trojan:Win32/Sirefef.AC is a risky Trojan that may bring many changes on the infected computer. Once this threat is inside the system, it can freely alter settings on desktop, add other malware, and modify the registry to run harmful codes when Windows starts. Normally, main payload of Trojan:Win32/Sirefef.AC is to drop other threats including malware, viruses, and spyware. It is known to redirect Internet search to malicious web sites so that user instantly acquire other malware.

Once it points the browser to unsafe web pages, Trojan:Win32/Sirefef.AC can execute other codes without alerting your anti-virus program. It is using an advanced technique called rootkit to hide its presence on the computer. Moreover, it can kill any running processes that belong to security software including anti-malware and anti-virus. Though, some effective security solution can survive with the attack caused by this Trojan.

Computers infected with Trojan:Win32/Sirefef.AC may observed various symptoms. Some may see least signs like browser hijacking, while other PCs may suffer from eminent malfunction leading to blue screen of death (BSOD). With the use of more hazardous malware, damages caused by this Trojan can be permanent. When it happens, reformat is the only solution to fix the computer.

As a first aid to remove the infection, we first suggest to restore your Windows to previous settings. If it is not possible due to serious issues cause by Trojan:Win32/Sirefef.AC, then, you need to run a couple of scans using various tools. Please see the guide below for complete procedures.

What are the Symptoms of Trojan:Win32/Sirefef.AC infection?

With the rootkit technique used by Trojan:Win32/Sirefef.AC, some security programs may detect its presence. However, there are efficient tool that can identify and prevent the attack. See image below for reference.


Procedures to Remove Trojan:Win32/Sirefef.AC

Removal steps on this page will help you get rid of the threat effectively using tools and virus scanners. Please make sure that you will carry out the guide in exact order.

Procedure 1: Scan Computer in Safe Mode Using Installed Anti-virus Program

1. When troubleshooting a PC, one common step is to boot operating system into Safe Mode with Networking. The same approach will be used in the removal of Trojan:Win32/Sirefef.AC. Please execute instructions based on your Windows OS version.

Start Windows 8 / Windows 10 in Safe Mode with Networking

- Close all running programs on your computer because we will need to restart Windows on this procedure.
- Press and Hold Shift key on your keyboard while clicking on Restart.
- You will then be presented with Troubleshooting Options.
- Click on Troubleshoot icon.
- Then, Click on Advanced Options icon.
- Select Startup Settings icon and then, Click on Restart button.
- When Windows restarts, it will prompt to choose number from the list of options. Press the number on your keyboard that corresponds to Safe Mode with Networking, commonly number 5.
- Once in Safe Mode, please proceed to the next step which is running a virus scan on the computer.

Start in Safe Mode with Networking (Windows XP / Vista / 7 Instruction)

- Please restart the computer and just before Windows start, press F8 on your keyboard repeatedly. You will be presented with Advanced Options Menu.
- From the selections, choose Safe Mode with Networking. Please use keyboard's arrow up/down to navigate between selections and press Enter to proceed.


2. Once your Windows is running in Safe Mode, open your installed anti-virus programs and update it to the most recent version by automatically downloading necessary updates.

3. Thoroughly scan the computer and remove all identified threats. Do not restart or turn off the computer after the scan process. You still need to run another scan. Please follow the next procedure.

Procedure 2: Scan and remove Trojan:Win32/Sirefef.AC files with MalwareBytes Anti-Malware

To remove Trojan:Win32/Sirefef.AC, download Malwarebytes Anti-Malware. This tool is effective in getting rid of Trojans, viruses and malware.

Download MalwareFox

1. After downloading, please install the program using the default settings.

2. At the end of the installation, please make sure that it will download necessary updates.

3. Once update has completed, MalwareFox will launch.

MalwareFox Scanner

4. Select SCAN button of MalwareFox application.

5. Scanning process will start and infections list will be displayed. Click NEXT to remove them.

MalwareFox Detection Result

Procedure 3: Run extra scan with Junkware Removal Tool

To make sure that no more malicious files linked to Trojan:Win32/Sirefef.AC are inside the computer, we must run another effective scanner. This time, use Junkware Removal Tool. No installation is necessary with this tool.

Download JRT

1. Click the button above to start the download process. Save the file to your preferred location.

2. Junkware Removal Tool will close all running applications later. So, before executing the file, please Bookmark or Print this page. And then, close all programs.

3. Double-click the JRT.exe file to initiate the tool.

4. It will prompt you to "Press any key to continue."

JRT Scanner

5. Junkware Removal Tool will create a Restore Point and proceed with the scan. Please wait for the scan process to finish.

6. After scanning the computer, JRT will open a Notepad containing scan logs. It may have not find Trojan:Win32/Sirefef.AC relevant entities, but it will surely delete any malicious items not found in the previous scans.

Procedure 4: Reset Affected Internet Browser

Reset browser settings of Google Chrome:

1. Open Google Chrome browser.

2. In the address bar, type this: chrome://settings/ and then, press Enter.

3. Navigate at the end of the page and click on Show advanced settings.

4. At the bottom of the page, click on Reset settings to remove all changes made by Trojan:Win32/Sirefef.AC.

Reset Google Chrome

Reset Internet Explorer Settings:

1. Open Internet Explorer software.

2. Navigate to top menu and click Tools > Internet Options.

3. On Internet Options window, select Advanced tab.

4. In order to reverse modifications caused by Trojan:Win32/Sirefef.AC, click on Reset button to bring back Internet Explorer's settings to their default condition.

Internet Explorer

Reset Firefox to its default state:

1. Open Mozilla Firefox program.

2. Navigate to top menu and Open Help Menu. Then, select on Troubleshooting Information.

3. Click on Refresh Firefox button to erase the effect of Trojan:Win32/Sirefef.AC.

Reset Firefox

Protect your PC from Trojan:Win32/Sirefef.AC or Similar Attack

Turn On Safe Browsing Features

Google Chrome's Protection from Dangerous Sites

With Google Chrome's Dangerous Site Protection feature, you will have lesser risks browsing the web. It will display a warning when the site you are trying to visit is suspicious, thus, you can prevent Trojan:Win32/Sirefef.AC infection. To enable protection from dangerous sites, please do these steps:

1. Open Google Chrome.

2. In the address bar, type this: chrome://settings/ and then, Press Enter.

3. Once on the settings page, click on Show advanced settings... at the bottom of the page to see the rest of the Chrome setup.

4. Locate Privacy section and mark 'Protect you and your device from dangerous sites'.

Chrome Security Settings

5. Please restart Google Chrome. New settings keep your browser safe while surfing the web.

SEE MORE : Enable Google Chrome's protection from dangerous sites

Internet Explorer - Activate SmartScreen Filter

Internet Explorer versions 8 and 9 has this feature called SmartScreen Filter. It helps detect phishing web sites and protect you from downloading malicious programs including Trojan:Win32/Sirefef.AC. To turn on SmartScreen Filter, follow these steps:

1. Please open Internet Explorer.

2. On top menu, select Tools (IE 9). For IE 8, please look for Safety menu.

3. Select SmartScreen Filter from the drop-down list and click on Turn on SmartScreen Filter.

IE SmartScreen Filter

4. Please restart Internet Explorer.

SEE MORE : Comprehensive steps to activate SmartScreen Filter

Mozilla Firefox - Block Attack Sites and Web Forgeries

Phishing and Malware Protection is a built-in feature on Firefox version 3 or later. It warns you when a page you are trying to visit contains phishing content or an attack site designed to drop threats such as Trojan:Win32/Sirefef.AC. To help you keep safe while browsing the Internet using Firefox, please follow this guide:

1. Open Mozilla Firefox browser.

2. On top menu, click on Open Menu. Then select Options from the list.

3. Select Security and put a check mark on the following items:

  • Warn me when sites try to install add-ons
  • Block reported attack sites
  • Block reported web forgeries

Firefox Security Settings

Edge Browser - SmartScreen Filter

SmartScreen filter is a built-in feature in Microsoft Edge browser that can help you deter malicious programs such as Trojan:Win32/Sirefef.AC. It can block malicious web sites and downloads.

1. Open Microsoft Edge browser.

2. Click on More Actions button located at top right corner of the screen.

3. Select Settings from the drop-down list.

4. Under Settings menu, go to Advanced Settings section and click on View Advanced Settings.

5. Scroll down to "help protect my PC from malicious sites and downloads with SmartScreen Filter". Turn it to ON.

6.You may now restart Microsoft Edge browser.

Edge SmartScreen Filter

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