SecurityFocus reports an estimated 3.5 million computers have been compromised due to a “Downadup worm,” a malicious bot that spreads through websites and blogs.

The Downadup worm, a malicious program that spreads using a recently patched Windows flaw, has compromised more than 3.5 million computers, security firm F-Secure stated this week.

The Downadup worm has successfully spread because it uses a major flaw that Microsoft patched in October to remotely compromise computers running unpatched versions of the Windows operating system. However, the malicious program’s greatest strength appears to be a feature that allows worm-controlled computers to download malicious code from a random drop point.

The program generates addresses for 250 different domains each day. The botnet controller need only register one of the domains and set up a download server to update the bot program with different functionality, said Mikko Hyppönen, chief research officer at F-Secure.

“The bad guys only need to predetermine one possible domain for tomorrow, register it, and set up a website, and they then gain access to all of the infected machines — pretty clever,” Hyppönen said in a blog post.

According to the report, the Downadup worm uses Windows XP’s vulnerability in processing remote procedure call (RPC) requests. While a patch was issued and warnings announced, not everyone has upgraded. The top countries hit by the MS08-067 Worms, as F-Secure calls them, are China, Brazil, and Russia, but it is expected to spread further unless server administrators and webmasters update and patch their Windows Servers and Windows programs immediately, including Internet Explorer.

ZD-Net Security Threats reports that the first sign of infection is usually found when users accounts cannot access their accounts and they are locked out of the Active Directory domain as the worm tries to crack passwords in Windows Servers.

Tracking the Downadup infection, F-Secure reported that reports of infections are up by more than one million within just one day, and growing. As last check, they estimate 3,521,230 infections worldwide. [Read more…]