Sasser worm

Sasser is a computer worm that affects computers running vulnerable versions of the Microsoft operating systems Windows XP and Windows 2000. Sasser spreads by exploiting the system through a vulnerable port. Thus it is particularly virulent in that it can spread without user intervention, but it is also easily stopped by a properly configured firewall or by downloading system updates from Windows Update. The specific hole Sasser exploits is documented by Microsoft in its MS04-011 bulletin, for which a patch had been released seventeen days earlier.

Sasser was first noticed and started spreading on April 12, 2004. This worm was named Sasser because it spreads by exploiting a buffer overflow in the component known as LSASS (Local Security Authority Subsystem Service) on the affected operating systems. The worm scans different ranges of IP addresses and connects to victims' computers primarily through port 445. Microsoft's analysis of the worm indicates that it may also spread through port 139. Several variants called Sasser.B, Sasser.C, and Sasser.D appeared within days (with the original named Sasser.A). The LSASS vulnerability was patched by Microsoft in the April 2004 installment of its monthly security packages, prior to the release of the worm. Some technology specialists have speculated that the worm writers reverse-engineered the patch to discover the vulnerability, which would open millions of computers whose operating system had not been upgraded with the security update.

The effects of Sasser include the news agency Agence France-Presse (AFP) having all its satellite communications blocked for hours and the U.S. flight company Delta Air Lines having to cancel several trans-atlantic flights because its computer systems had been swamped by the worm. The Nordic insurance company If and their Finnish owners Sampo Bank came to a complete halt and had to close their 130 offices in Finland. The British Coastguard had its electronic mapping service disabled for a few hours, and Goldman Sachs, Deutsche Post, and the European Commission also all had issues with the worm. The X-ray department at Lund University Hospital had all their four layer X-ray machines disabled for several hours and had to redirect emergency X-ray patients to a nearby hospital. The University of Missouri was forced to "unplug" its network from the wider Internet in response to the worm.

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