<https://forums.malwarebytes.com/topic/163619-mbr-rootkit-prevents-any-av-including-mbar-from-running/>
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"I have a Win7(x64) system that was badly infected with multiple viruses. Although I was able to manually stop all visible malicious processes and clean out all visible malicious files and reg entries, I could never get a single AV or malware tool to run. Not mbar, not any of numerous AV's I tried, not gmer, not tdsskiller, not rkill, etc etc etc. If you clicked on the exe's, they would just start and immediately close. Renaming the exe's or changing the extensions to com also didn't work. Oddly, hijackthis would run but indicated nothing. Taskmanager and regedit worked as well.   Thinking I had simply missed a rootkit, I decided to nuke the OS. It was a Dell OptiPlex with a recovery partition, so throwing back to factory was easy. The system was somewhat old and not cost effective to do a disk reinstall.   After re-imaging the OS partition to factory, all was going well until I saw that built in Windows defender wouldn't update. I tried loading AVG AV and that wouldn't run. MBAR nada. Clicking on the exe's would result in the installer opening and closing instantly, as before reload.   There must be some sort of mbr or sector zero rootkit whose purpose is just to prevent any av or malware tool from running.   Any last ditch suggestions from you guys? Some sort of boot disk or usb key with mbar on it? By the way, Kaspersky rescue disk and Norton Power Eraser run as boot media detected nothing. I don't believe fixmbr from the Windows recovery media will work because the Dell mbr is not standard (although I am going to try it).   I know I can probably write zeros to the entire HD or low level format and reload from disk, but it just wouldn't be cost effective as mentioned before. I know there are times when you have to give up, but I hate to admit defeat on this one. I've only had to do it twice before. Sometimes when you put in a lot of effort it becomes personal.   Thanks!   Joe Welna "
<https://forums.malwarebytes.com/topic/163619-mbr-rootkit-prevents-any-av-including-mbar-from-running/>