MSE Install fails with 0x8004FF91

Well, this was an annoying one, and it’s hard to find the one thread that actually addresses it amongst the ones conflating it with an off-by-one error code (subtract one from 0x8004FF91. not going to actually say it here to avoid poisoning Google).

TL;DR if you can’t install Microsoft Security Essentials – even on a […]

how malware prevents programs from running

In today’s battle with malware, I learned a couple of interesting new places in the registry to check:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options

Place a key in here named after the file you want to prevent running, then place a STRING value under the key named “debugger”. Now, set the value of “debugger” to cmd, […]