Some viruses behave in such a manner that you realise immediately that they have infected your system, but others can behave like common system problems, making the presence of a virus difficult to determine. Viruses can make your system behave strangely, but this behaviour could also be due to an application error, a driver problem or hardware malfunctions.
A virus can make strange things appear on the screen, but so can driver problems or an incorrect BIOS setting. Similarly, a virus can cause the system to reboot, but so can faulty power supplies, an operating system problem or an overheating processor.
Because a virus infection can often duplicate the symptoms of a hardware or software problem it is a good idea to carry out a virus scan before taking further troubleshooting steps, even if all it does is eliminate viruses as the source of the problem. The following symptoms are often a result of genuine hardware or software problems, but can also be caused by viruses:
- Spontaneous system reboots
- System crashes/hangups
- Application crashes/hangups
- Sound problems
- Screen glitches
- Corrupted data
- Disappearing partitions
- Slow operation
- Boot failure
Some types of system behaviour strongly suggest the presence of a virus, eg:
- Strange Messages: if you boot your PC and see the message the message "Your PC is now Stoned!" you can be fairly certain that you have a virus.
- Text Behaviour: If DOS text starts moving around on the screen, letters keep changing colour or ASCII graphics move around the screen deleting other characters, there is a high probability that you have a virus.
- Strange Sounds: some viruses can generate music or strange tones on the system speaker.
- Changing File Sizes or Time/Date Stamps: file-infector viruses often increase the size of infected files and can also affect date/time stamps.
- Disappearing Files: if a recently-used file or program suddenly seems to have disappeared a virus may have deleted it.
Next: Virus Hoaxes