I've got a computer that runs Avast free version on it. I had an older version where I updated the definitions only, not the software itself. I don't 100% lock it down because I expect to be able to use it for various personal and gaming related tasks. So I clean it up and keep it relatively trim, but I don't get paranoid.
I mostly kept the old Avast free software with new definitions because it added some popups and a bit of interface bloat that I disliked, but the quality of the AV protection is still good. So a little while ago I accidentally told it to update the software and it did, but I didn't want to try ripping it out to go back to the old one. With Avast that can be a pain.
However, apparently the new version of Avast (the one it updated to) royally fubars some systems' VC+ redistributables and couple with a change or two MS did with how those were handled (so I have read) it hoses the DLLs. Some are missing and can't be used by a number of programs. You get missing DLL errors trying to run things from various people up to and including iTunes (yes, I know, iTunes). I have tried everything possible including the MS KB2999226 hotfix. Nothing works. I ripped out Avast and reinstalled the older version but the damage is done. The MS website no longer has the 2015 VC redist installer (apparently that's the main culprit for most of the stuff I've tried to run that gave me errors). I couldn't even try installing older VCs because they said they weren't the newest version. I uninstalled the 2017, 2016, 2015, then reinstalled the 2015, but it won't take now.
The KB patch says it's not applicable to my computer but I don't have it installed and it clearly is applicable. I have gone in circles for a day trying to research this one and find a solution. There isn't one that has worked so far. I manually downloaded a x86 and x64 for the first missing DLL and put them in system32 and syswow64, but then the next DLL was missing and I've been down this road before. I replace one and it'll say the next is missing. I need to restore the entire pack.
Speaking of: I don't want to reformat. I don't have a clean ghost on this. I don't want to repair and then lose a bunch of program associations, which has happened sometimes in the past. I don't have a restore point because I 1) don't trust MS restore and 2) keep those pared down to reduce HDD storage waste, 3) don't know exactly when the DLLs were hosed so can't back track to a proper pre-hosed savepoint. I'm looking for wisdom or help (or links to the above) on how to fix in-place.