Trojan:Win64/Sirefef.B is a trojan that connects to a remote server to download arbitrary files which can include malware, such as other components of Sirefef, and may be present on an affected computer as a file named "consrv.dll".

Trojan:Win64/Sirefef.B 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.

What to do now

Win32/Sirefef is a dangerous threat that uses advanced stealth techniques to hinder its detection and removal. If you are infected with Sirefef, we recommend you take the following steps to remove it.

Download and run the Microsoft Safety Scanner

Before you begin you will need:

  • A PC that is not infected and is connected to the Internet. You will use this PC 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 PC
  1. Download a copy of the Microsoft Safety Scanner from a clean, uninfected PC
  2. Save a copy of the Scanner on a blank CD, DVD, or USB drive
  3. Restart the infected PC
  4. Insert the CD, DVD, or USB drive into your infected PC and run the Scanner
  5. Let the Scanner clean your PC and remove any infections it finds

After running the scanner, make sure your antivirus software is up-to-date. You can update Microsoft security software by downloading the latest definitions.

The following Microsoft products detect and remove this threat:

Note that as part of the cleaning, our software might change some Windows services back to their default settings. If you had previously changed these settings, you might need to change them again.

The services that are reset include:

  • BFE – Base Filtering Engine
  • Iphlsvc – IP helper Service
  • MSMpSvc – Microsoft Antimalware service – MSE/FEP/SCEP
  • Sharedaccess – Internet Connection Sharing
  • WinDefend – Microsoft Antimalware service
  • Wscsvc - Windows Security Center

Threat behavior

Trojan:Win64/Sirefef.B is a trojan that connects to a remote server to download arbitrary files which can include malware, such as other components of Sirefef.


This trojan is installed by other malware, such as Trojan:Win64/Sirefef.A, and may be present on an affected computer as the following file:

  • %windir%\System32\consrv.dll

The trojan is injected into the process "svchost.exe" and its payload is executed.


Downloads arbitrary files
Trojan:Win64/Sirefef.B connects to a remote server to retrieve commands that could include the following actions:

  • download arbitrary files or updated Sirefef components
  • execute retrieved files
  • inject retrieved files into other processes

Analysis by Shawn Wang


System changes

The following system changes may indicate the presence of this malware:

  • The presence of the following files:
  • Alert notifications from installed antivirus software may be the only symptoms.


Alert level: Severe
First detected by definition:
Latest detected by definition: 1.203.795.0 and higher
First detected on: Jun 21, 2011
This entry was first published on: Jun 21, 2011
This entry was updated on: Sep 02, 2013

This threat is also detected as:
  • BackDoor.Maxplus.23 (Dr.Web)
  • ZeroAccess.b (McAfee)
  • Zero Access rootkit (other)
  • Max++ (other)
  • ZAccess (other)