I hate antivirus software with a passion. I've wasted too many weeks of my life hacking around bugs that antivirus programs introduced into my customers' systems.<p>A couple I've dealt with in the last six months:<p>McAfee Antivirus causes applications built with Unity 4 to fail when they call WWW.LoadFromCacheOrDownload() on a large asset bundle. This API call downloads a temp file and then renames the file to move it into the cache. But McAfee also opens the file for a virus scan. For a large file, the virus scan may not complete before Unity tries to rename the file, so the rename fails and you never get the asset bundle.<p>For one client I fixed this by patching Unity's .exe file to add a retry loop on the rename call. Unity 5 also works around this issue with the same retry loop.<p>AVG Antivirus causes updates to fail for applications that use wyUpdate. wyUpdate calls the CreateMutex() function in the Windows API to make sure another updater instance isn't already running. Bizarrely, when AVG is installed, CreateMutex() returns the wrong value, so wyUpdate thinks another instance is running and bails out. No updates for you!<p>Going back a few years, I tried NOD32 after some friends recommended it. It seemed fine, except the Alt+Tab key no longer worked. It was a known bug, unfixed for some time.<p>About 5-6 years ago, McAfee had a known bug - unfixed for nearly a year - than under some circumstances it would erase the entire hard drive. This was the ultimate in virus protection!