I'm using Symantec Antivirus 10.0, for some reason, when I updated it to the new definitions which is 4/29, it would revert back to 4/12 definition files, and a message would display saying my definitions could not be found and my system was not fully updated. Since I couldn't find where they are stored, I downloaded the new definitions and installed them in C:\Program Files\Symantec AntiVirus and so far, so good. But do you know where they are stored?