It's worth noting that this article has a link to a detection and removal tool for the trojan: http://macscan.securemac.com/files/iServicesTrojanRemovalToo...

So how do you tell whether you have this trojan or not? Is there an easy way to check?

If you have torrented software (photoshop cs4 or iwork 09) then you need to download the checker and remover from securemac.com: http://macscan.securemac.com/files/iServicesTrojanRemovalToo.... If not you shouldn't have anything to worry about.