MBP is eating its own programs

My fiance’s 2008 Macbook Pro has been deleting programs, and I have no idea why. The icons will still appear on the menu bar, but with a ‘?’ imposed on top of them. When I search the system to locate the program, I can’t find anything. I know she hasn’t manually deleted them, or done anything other than use the computer as she usually does. First to go was Photo Booth, then iMovie and Garage Band, now it looks as though Photoshop has fallen victim. I know Mac viruses are a rare thing, but could that be a possibility? A corrupted OS maybe? If anyone has heard of something like this before I’d love some insight. Thanks!

By "menu bar" I'm assuming you're referring to the Dock? The icons that appear on the Dock are aliases which point back to the original programs that are located in the "Applications" folder. Have you looked in the Applications folder to see if the programs are still there? If they don't show up in the Applications folder, then they may in fact be gone.

The system does not delete programs on its own. And since there are no known viruses for the Mac (please read forum sticky LINK) someone or something deleted them. Has she done any updates lately? Installed new software?