Although you didn't say so, assuming you're using Windows, you may be able to "restore" System files by going to Control Panel|Programs and click the "Turn Windows Features On and Off." Reselect the options you want, and run, and sometimes Windows will replace any missing System files needed for your setup.

You have to have left the "installation files" on your hard drive, or if they've been deleted you'll need an installation or recovery disk to get the files from.

As MMario says though, if you haven't noticed they were gone you probably don't really need them for what you've been doing.

You may be able to look in the quarantine space and see what files are there. Make a list and you'll at least know what to look for if you decide you need to restore them later.

John