Microsoft security software detects and removes this threat.

This threat is a member of the Win32/Sefnit family. This family can hide on your PC and do different things, including:

• Downloading and running other files
• Contacting remote hosts
• Disabling security features

They can also change your search results, which can generate money for malicious hackers.

Variants of Win32/Sirefef might be installed by other malware, including variants of the Trojan:Win32/Necurs family.

Windows Defender Antivirus detects and removes this threat. See the Win32/Sirefef description for more information.

Trojan:Win32/Sirefef.K is a component of Win32/Sirefef - a multi-component family of malware that moderates your Internet experience by changing search results and generating pay-per-click advertising revenue for its controllers. The family consists of multiple parts that perform different functions, such as downloading updates and additional components, hiding existing components, or performing a payload.

Trojan:Win64/Sirefef.K is the 64-bit user-mode component of Win32/Sirefef - a multi-component family of malware that moderates your Internet experience by changing search results and generating pay-per-click advertising revenue for its controllers. The family consists of multiple parts that perform different functions, such as downloading updates and additional components, hiding existing components, or performing a payload.

Virus:Win32/Sirefef.N is a component of Win32/Sirefef - a multi-component family of malware that moderates your Internet experience by changing search results and generating pay-per-click advertising revenue for its controllers. The family consists of multiple parts that perform different functions, such as downloading updates and additional components, hiding existing components, or performing a payload.

Caution: Win32/Sirefef is a dangerous threat that uses advanced stealth techniques in order to hinder its detection and removal. If you are infected with Sirefef, we recommend you take the following steps to remove this threat from your computer:

Before you begin you will need:

- A computer that is not infected and is connected to the Internet. You will use this computer to download a copy of the Microsoft Safety Scanner
- A blank CD, DVD or USB drive. You will use this CD, DVD or USB drive to run the Scanner on your infected computer 

1. Download a copy of the Microsoft Safety Scanner from a clean, uninfected computer
2. Save a copy of the Scanner on a blank CD, DVD, or USB drive
3. Restart the infected computer
4. Insert the CD, DVD, or USB drive into your infected computer and run the Scanner
5. Let the Scanner clean your computer and remove any infections it finds

After running the Scanner, ensure that your antivirus product is up-to-date. You can update Microsoft security products by downloading the latest definitions at this link: Get the latest definitions.

As a consequence of being infected with this threat, you may need to repair and reconfigure some Windows security features. Please see Additional remediation steps in this entry for more information.

TrojanDownloader:Win32/Sirefef.E is a component of Win32/Sirefef - a multi-component family of malware that moderates your Internet experience by changing search results and generating pay-per-click advertising revenue for its controllers. The family consists of multiple parts that perform different functions, such as downloading updates and additional components, hiding existing components, or performing a payload.

Caution: Win32/Sirefef is a dangerous threat that uses advanced stealth techniques in order to hinder its detection and removal. If you are infected with Sirefef, we recommend you take the following steps to remove this threat from your computer:

Before you begin you will need:

- A computer that is not infected and is connected to the Internet. You will use this computer to download a copy of the Microsoft Safety Scanner
- A blank CD, DVD or USB drive. You will use this CD, DVD or USB drive to run the Scanner on your infected computer 

1. Download a copy of the Microsoft Safety Scanner from a clean, uninfected computer
2. Save a copy of the Scanner on a blank CD, DVD, or USB drive
3. Restart the infected computer
4. Insert the CD, DVD, or USB drive into your infected computer and run the Scanner
5. Let the Scanner clean your computer and remove any infections it finds

After running the Scanner, ensure that your antivirus product is up-to-date. You can update Microsoft security products by downloading the latest definitions at this link: Get the latest definitions.

As a consequence of being infected with this threat, you may need to repair and reconfigure some Windows security features. Please see Additional remediation steps in this entry for more information.