Published Nov 11, 2004 | Updated Apr 16, 2011


Severe |Detected with Windows Defender Antivirus

Aliases: W32/Sasser.worm (McAfee) W32.Sasser.Worm (Symantec) WORM_SASSER (Trend Micro) Win32.Sasser (CA) Sasser (F-secure) Sasser (Panda) W32/Sasser (Sophos) W32/Sasser (Norman)


Win32/Sasser is a family of network worms that exploit the Local Security Authority Subsystem Service (LSASS) vulnerability fixed in Microsoft Security Update MS04-011. The worm spreads by randomly scanning IP addresses for vulnerable machines and infecting any that are found.
Recovering from recurring infections on a network
The following additional steps may need to be taken to completely remove this threat from an infected network, and to stop infections from recurring from this and other similar types of network-spreading malware:
  1. Ensure that an antivirus product is installed on ALL computers connected to the network that can access or host shares.
  2. Ensure that all available network shares are scanned with an up-to-date antivirus product.
  3. Restrict permissions as appropriate for network shares on your network. For more information on simple access control, please see:
  4. Remove any unnecessary network shares or mapped drives.
Note: Additionally it may be necessary to temporarily change the permission on network shares to read-only until the disinfection process is complete.
Removing this threat
To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as Microsoft Security Essentials, or the Microsoft Safety Scanner. For more information about using antivirus software, see
Follow us