I have a customer's laptop computer which was badly infected with Vundo, MyWebSearch, and a couple additional Trojans. Booted to a known clean hard drive and scanned with up-to-date AVG and killed all found infections. (Note: McAfee had been running on the computer for nearly a year and virus definitions were up-to-date, but all of the infections were allowed to install and McAfee did not detect them in scans.) While in the clean system I deleted all infection folders as well as all IE temp files and other temp files where infections often hide. Then I returned the drive to the laptop and ran a scan with MalWareBytes and deleted all the found infected registry entries (no additional infections were found). Now almost any Microsoft routine I try to run generates "An unidentified program wants access to your computer" User Account Control alerts -- including regedit, msconfig. defrag, scan drive for errors, event viewer, etc. I initially suspected a rootkit, but scans with two rootkit detectors (Blacklight, Sophos) found nothing. What can cause the User Account Control to be unable to identify Microsoft's own routines as known and safe? I'm assuming that something's corrupted or that there's a rootkit that hasn't been found. My next step would be to try to run a repair installation, but this is Vista Home Basic and the customer has no installation disk (this is a Dell laptop). Two questions: 1. Any suggestions on what could be causing this problem of Vista being unable to identify its own routines? 2. If I am to do a repair installation, I never sold Vista so don't have copies of any Vista installation disks. I have only the following Vista files: a. TechNet download of Windows Vista (x86) b. a copy of Windows Vista Business 32-bit Dell installation disk c. a copy of the recovery partition files from this laptop computer Can any of these be used to do a repair installation of OEM Vista Home Basic? More than anything, I'd like to know what could cause this User Account Control behavior....