Symptoms and Effects
It can be difficult to determine if your computer is infected with a virus, which is why it is necessary to have a reliable anti-virus software installed on your computer. There are however symptoms that you can look for which indicate the possible presence of a virus. A virus infection can cause the following symptoms, but keep in mind that these symptoms can also be the result of other problems on your computer.
The computer shuts down and restarts for no apparent reason.
The computer takes a long time to start and runs very slowly. This can be caused by having too many programs open, problems with the network, but also by a virus infection.
Sudden reduction in disk space or memory capacity. This may be an indication of a virus infection as viruses can sometimes consume all available free space.
If the same file appears twice, one with an .EXE extension and the other with a .COM extension, it is very likely that the second file is infected.
A file is missing, it cannot be opened, or there is an unexpected change in the file's properties. Viruses can delete files or alter them, making them unusable.
A program closes suddenly for no apparent reason, it won't run, or your computer stops responding when you try to use the program. Viruses can alter or delete files associated with a specific program causing it to no longer function properly.
The anti-virus program is disabled and cannot be restarted.
Strange messages or dialog boxes appear on the screen.
Other strange effects that can be indications of a virus infection include the CD-ROM tray opening and closing, keyboard and mouse actions taking place automatically, and windows appearing and disappearing at random.