CWmike writes "Microsoft has clarified the advice it gave users whose Windows PCs are infected with a new, sophisticated rootkit dubbed Popereb that buries itself on the hard drive's boot sector, noting Wednesday that a complete OS reinstall is not necessary. 'If your system is infected with Trojan:Win32/Popureb.E, we advise fixing the MBR using the Windows Recovery Console to return the MBR to a clean state,' MMPC engineer Chun Feng wrote in an updated blog entry. Feng provided links to instructions on how to use the Recovery Console for Windows XP, Vista and Windows 7. Once the MBR has been scrubbed, users can run antivirus software to scan the PC for additional malware for removal, Feng added. Several security researchers agreed with Microsoft's revisions, but a noted botnet expert doubted that the advice guaranteed a clean PC. But an internationally-known botnet expert disagrees. Joe Stewart, director of malware research at Dell SecureWorks, said, 'Once you're infected, the best advice is to [reinstall] Windows and start over ... [MBR rootkits] download any number of other malware. How much of that are you going to catch? This puts the user in a tough position.' MBR rootkit malware is among the most advanced of all threats."