We've seen worse than Sasser - MS

Microsoft is considering automating the process of cleaning up systems infected by the Sasser worm, which spread like wildfire across the Internet over the weekend.

The software giant has already released a cleaning tool that can be downloaded manually. Microsoft may put this into automatic updates, depending on the "level of infection and feedback from ISPs," Stuart Okin, Chief Security Officer at Microsoft UK, told El Reg.

The idea is the same as with a Blaster clean-up tool released in January: create a utility to clean PCs that have been patched against the vulnerability it exploited, but are still infected with the worm. Microsoft now has the systems in place to roll out the disinfection much more quickly this time, if necessary. A decision depends on the extent of Sasser's scanning activity.

Sasser is a network aware worm that exploits a recently announced Microsoft vulnerability (in Windows Local Security Authority Subsystem Service Microsoft vulnerability - MS04-011). The worm, and its three variants - so far - spreads by scanning randomly chosen IP addresses for unpatched systems to infect. A patch was released last month.

Worst Windows worm ever?

Okin said the effects of Sasser are less than that of Blaster. Most of the calls Microsoft is getting, at least from the UK, are from consumers. The software giant has drafted in extra staff to man the phones. Microsoft UK reports that there have been no major outages for UK businesses even though the worm has caused significant problems elsewhere. Sampo, Finland's third largest bank, WestPac and RailCorp in Australia have all endured operational difficulties because of Sasser.

Symantec, the anti-virus software firm, has counted at least 10,000 confirmed infections. It reckons that "hundreds of thousands" of computers worldwide have been infected by Sasser. Kevin Hogan, senior security manager of Symantec security response, said that Sasser spread less quickly than Blaster but has affected more PCs.

Defensive measures are fortunately very simple. Users should turn on firewalls, apply patches and update AV signature files. Symantec recommends that enterprises block ports 5554, 9996 and 445 at the perimeter firewall and install the appropriate Microsoft patch (MS04-011) to prevent remote exploitation of the vulnerability.

Did NetSky authors create Sasser?

Text in recent versions of the NetSky worm (NetSky-AC) and Sasser as well as shared code between the two worms suggest each might be the work of the same author or authors. Okin refused to be drawn on speculating about this circumstantial evidence.

Microsoft is working with the relevant investigative authorities - such as the FBI in the US and the National Hi-Tech Crime Unit in the UK - to trace the culprits behind the release of the worm. ®

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