Viruses are fragments of program code that with the help of other programs are able to replicate. Contrary to popular belief they are not necessarily dangerous.
In most cases just taking a few sensible precautions will help to keep the problem down to a manageable level.
The level of paranoia that surrounds viruses is in the main due to ant-virus vendors deliberately hyping up the situation to generate more business.
If you do find that you have a virus DON'T PANIC. The situation is recoverable.
For more information on viruses please read my book Virus: A computer malaise. Feedback is very welcome, especially as I am currently working on the second edition. The book is only available direct from myself.
Internet is not only a source of viruses, it is also the place to go to for more information. My book contains an appendix listing sites. Any site not listed should contact myself for inclusion in the second edition.
Apart from reading my book I would also recommend a copy of my anti-virus software Anti-Virus. This is only available as shareware. To enable verification of my software you will need a copy of my PGP public key.
An international virus consultancy service is available.
Viruses are only one part of a more general security problem. For more information on another aspect of computer security please take a look at my PGP page.