If you see that your computer acts strangely, namely:
- abnormal messages and images are displayed;
- CD-ROM tray opens and closes unexpectedly;
- some programs are run arbitrarily on your PC;
- a message is displayed informing that some program is trying to connect to the Internet, though you have not initiated any actions.
then it is likely that your computer is virus-infected. See KB790 for other signs of computer infection.