Symantec, over the holidays, spotted another round of infections in the form of a worm known as W32.Downadup. Microsoft is terming the malware Win32/Conficker.
The latest variant finds a new way to take advantage of the highly critical bug, which involves the Remote Procedure Call (RPC) protocol, Symantec researchers said on Friday. In prior attacks, an attacker could execute remote code by sending a specially crafted RPC request.
However, the new exploit "can also spread through corporate networks by infecting USB sticks and accessing weak passwords," Symantec's Security Response department said Friday in a forum post.
"W32.Downadup.B creates an autorun.inf file on all mapped drives so that the threat automatically executes when the drive is accessed," according to Symantec. "The threat then monitors for drives that are connected to the compromised computer in order to create an autorun.inf file as soon as the drive becomes accessible."
On Oct. 23, Microsoft delivered a rare, out-of-cycle patch for the flaw, which was being actively exploited in targeted attacks.
Matt McCormack of the company's Malware Protection Center wrote on Dec. 31 that researchers have detected a new outbreak of the attack, mostly on machines that have yet to apply the patch.