Skip to main content
Skip to main content
Microsoft Security Intelligence
269 entries found. Displaying page 1 of 14.
Updated on Jul 30, 2011
Alert level: severe
Updated on Sep 20, 2015

Microsoft security software detects and removes this threat.

This family of malware uses stealth to hide its presence on your PC. Trojans in this family can do different things, including:

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

Members of the family can also change search results, which can generate money for the hackers who use Sirefef.

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

Find out ways that malware can get on your PC.

Alert level: severe
Updated on May 12, 2014

Windows Defender detects and removes this threat.

See the Win32/Sirefef family description for more information.

Alert level: severe
Updated on May 13, 2014

Windows Defender detects and removes this threat.

See the Win32/Sirefef family description for more information.

Alert level: severe
Updated on Sep 02, 2013

TrojanDropper:Win32/Sirefef.B is a trojan that drops 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.

Alert level: severe
Updated on Sep 02, 2013

TrojanDropper:Win32/Sirefef.gen!A is a trojan that is used to install Win32/Sirefef. It is distributed using exploits and social engineering tactics, where it is bundled with "keygens" and "cracks".

In a typical scenario, you may choose to download what they think is a "keygen" or "crack" (a program that enables software piracy by bypassing licensing or activation requirements). However, TrojanDropper:Win32/Sirefef.gen!A is also included in the download and is installed on your computer  - without your knowledge - alongside the keygen or crack. 

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.

Alert level: severe
Updated on Sep 02, 2013

TrojanDropper:Win32/Sirefef.A 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.

Alert level: severe
Updated on Sep 04, 2013

TrojanDropper:Win32/Sirefef.A!dll 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.

Alert level: severe
Updated on Sep 02, 2013

TrojanDropper: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.

Alert level: severe
Updated on Apr 18, 2013
Alert level: severe
Updated on Oct 14, 2023
Alert level: severe
Updated on Aug 03, 2012
Alert level: severe
Updated on Aug 06, 2015
Alert level: severe
Updated on Jul 06, 2012
Alert level: severe
Updated on Feb 07, 2012
Alert level: severe
Updated on Sep 23, 2010
Alert level: severe
Updated on Jan 10, 2012
Alert level: severe
Updated on Oct 24, 2023
Alert level: severe
Updated on Nov 05, 2013
Alert level: severe
Updated on Dec 07, 2012
Alert level: severe