On Tuesday, Microsoft started detecting Zeus with its Malicious Software Removal Tool (MSRT) -- a widely used virus removal program that's free for Windows users. That should make it harder for the many criminals who use Zeus to keep running their software on computers that don't have antivirus software installed -- often an easy target up until now.
According to a September 2009 study by security vendor Trusteer, 45 percent of Zeus-infected machines have either no antivirus software or an out-of-date product. On the other hand, Zeus has been effective at avoiding the type of detection that Microsoft is now adding to its MSRT. According to that same report, 55 percent of Zeus infections were on machines that did have working antivirus programs installed.
Microsoft wasn't available to talk about the MSRT by press time, Tuesday.
In a series of raids starting Sept. 28, authorities in the U.K., U.S. and Ukraine arrested more than 100 members of the largest-known Zeus gang, but there are still probably dozens of smaller gangs in operation. Zeus is very easy to obtain online, and it has been adapted by many different criminals since it first popped up four years ago.