Ratters can access your webcam and spy on you, as well as keylogging and looking through all your files on your computer. The only way to be sure is to cover your webcam with a piece of black electrical tape and only uncover when using it. Scan regularly with something like:
…although even this program can’t find all hackers and keyloggers. Best practice is to use GMail to obtain your emails and to be careful about which Internet sites you visit. Stay away from lyrics sites.