Anti-virus software does mess up sometimes. About half a year ago, one morning suddenly all my IDEs started acting up, all the built projects no longer ran and debuggers stopped working. Obvious virus check - nothing. I re-installed the IDEs, no luck, then thought I'll just update the GDB (gnu project debugger). Still nothing. Then for some reason, it started to complain about some corrupt or missing file, I think, in the system32 folder or something. Some very basic file anyway that most apps need to run. The error message also contained some error code but Googling that turned up nothing. Then I tried a bunch of other things and got pretty desperate and thought about reformatting the drive and reinstalling Windows. Luckily, then I had to go out and got back that evening and decided to give Google another chance before reformatting. And what turned up, searching for that error code again, was that the last virus update my AV automatically installed was messed up and started interfering with Windows. The update had been released literally hours before I had installed it, so no-one had started a topic anywhere about it, hence I couldn't find anything usable when searching. But by the time I got back home in the evening, a thread had been started on the AV forums (somehow somebody linked the error to the AV software by uninstalling it or something, luckily) and a solution was provided by the devs. I had to disable automatic updates for a while, until they worked out a fix, but it helped. I mean, who could've thought AV updates can do that ..