A virus is a tiny program that attaches itself to other files on your Macintosh such as Applications, the Desktop File, and the System document, among others. The virus then replicates itself and spreads to programs and system documents on your hard drive and/or any disk you insert. Any infected disks coming from your infected machine will most likely infect whoever's machine it's inserted in, thus spreading the virus.
Why Should I Care?
You should care, but at the same time you shouldn't panic over the possibility of your Mac becoming infected. Some virus's are 'benign'. They don't intentionally destroy data on your machine, but sometimes play a joke or just stay hidden. Often these virus's contain errors or bugs causing your Macintosh to bomb and possibly result in the loss or corruption of data. Other virus's do intentionally cause damage, such as wiping your disk or scrambling your data. This can result in the loss of time and money attempting to reconstruct the data you had originally.
How Can I Protect My Mac From an Attack?
There are a number of virus protection programs out there, including commercial ones such as SAM, and shareware programs such as Gatekeeper and Disinfectant. Personally, I use Gatekeeper and Disinfectant. Gatekeeper loads at startup and is configured through a control panel. It keeps and eye out for known virus's, and keeps an watches for activities that might indicate an unknown virus. It then stops the virus from doing any damage. Disinfectant is an application that scans your hard disk and floppy disks for known virus's, or unknown strains of known virus's. It will then delete the virus and attempt to repair any damage it may have caused. Both are excellent and should be used religiously. They are available from most Bulletin Boards and Mac User Groups. Remember, if you find a virus, check ALL of your floppies. There is a good chance that at least some of them are infected and could reinfect your machine.
If you're bringing a file over to a friend's house on a disk, and worried that he/she/it might have a virus, simply lock the floppy (slide the plastic tab on the left hand of the disk facing you). There is now NO WAY a virus is going to get on that disk. You're completely safe!
See the next chapter for a listing of the current Mac virus's and what they do, as well as a little bit of history.
 
What is a Trojan Horse?
Trojan Horse's usually have the same function in life as a virus, with one very important difference. They cannot replicate themselves. They depend on people to give spread them around. Most Trojan Horses are disguised as programs, and some even go as far as to hide in a working, legitimate program. When this seemingly legitimate program is run the trojan horse will go to work doing mostly malicious deeds.
How Can I Protect My Mac From an Attack?
Being aware of what program's are trojan horses and then not running them is your best protection. Using suspicious activity monitors such as Gatekeeper or SAM will usually keep the trojan horse from doing any damage to your Macintosh.
See the Chapter "Trojan Horses" for a listing of current Macintosh trojan horse's.
