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I'm back to update you on our changes to Zbot in the Malicious Software Removal Tool (MSRT). We reviewed the data coming back from MSRT in September and incorporated the findings into October's MSRT (and beyond), which means we are now in a position to provide additional information.
As I mentioned in the previous blog post, the purpose of our special Zbot September update was to glean an insight into the effectiveness of MSRT against this prolific threat. Couple that with a focus on the Zbot family and, suffice it to say, we're pretty happy with our findings and results!
And now, onto the numbers!
Historically, and prior to the September 2011 release, MSRT consistently detected about 90% of PWS:Win32/Zbot variants in the wild. For the month of September 2011, we detected and removed PWS:Win32/Zbot from around 185,000 distinct Windows computers, a stark increase to the months beforehand, which we can attribute the increase to additional technology added to MSRT for just such an occasion.
For October so far, we've removed Zbot from over 88,000 computers and we expect that number to grow to around 100,000 - again, a very good result from MSRT, illustrated in the chart below that lists October 2011 MSRT data:
These increased numbers are also likely a result of new functionality we've seen in Zbot recently. It seems that some variants now automatically spread via the Windows autorun functionality; something that is very common with other prolific malware families, so it's not very surprising we're seeing it now - but is surprising we hadn't seen it before now. Regarding autorun, Microsoft released a security update in February of 2011 that changed its default behavior - the result was an overall decline in threats utilizing autorun as a spreading mechanism. There is a Microsoft Knowledge Base article that discusses how to disable autorun in Windows, here.
October 25th marked the tenth anniversary of the release of Windows XP. And what a difference a decade makes! Consumers should upgrade to the newest operating system version in order to take advantage of enhanced security features of Windows 7 including AppLocker, User Account Control (UAC), Data Execution Prevention (DEP) and Structured Exception Handling Overwrite Protection (SEHOP). The recently released Microsoft Security Intelligence Report volume 11 shows that the latest Windows 7, 32-bit OS is six times less likely to become infected than the comparable Windows XP SP3.
And finally a reminder, MSRT isn't a replacement for a full antivirus solution. You're already infected when MSRT detects malware – using a security application with real-time protection can help prevent you from becoming infected in the first place.
Matt McCormack MMPC Melbourne