If you want to test your Antivirus Scanner, you can use the test string from the European Institute for Computer Antivirus Research  “eicar“. Put this string into a file. Send it, download it, compress it, do what ever you want. Scan the file, see if your Antivirus scanner finds it.

Here the string.

X5O!P%@AP[4PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*

Even if your scanner finds this pattern, keep your scanner updated. It is like in real life. The dangerous ones are the unknown ones.

The links in the table blow contain the test string. The files are compressed with different methods.

Users coming from the UNIX side are used to a life without anti virus scanner. Microsoft users feel uncomfortable and naked, if they don’t have a virus scanner. This discrepancy always leeds to discussions about the need of an antivirus scanner on an Apple computer. If you ask the AV industrie, they say you need one. Of course, there is a lot of money to make in this market. Experience shows, today you do not really need one.
Currently there are three known trojans for Mac available. One of them only installs, if you get a cracked verison of iWork 09. Being a little bit careful from where you download your software from helps more then spending a lot of money for software, which just slows down your machine.
Starting with 10.6 Apple started to scan downloads for trojans. There is a file called

/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/XProtect.plist

on your Mac containing the signatures of these three known trojans.
Anyway. Currently it is not necessary to spend a lot of money for virus protection on a Mac. If you want to scan your Mac from time to time, get the open source antivirus scanner clamav, with comes nicely packed with a nice frontend in a package called ClamXav. Download the free version and scan your Mac from time to time.

More information to this subject can be found here.