Malware are now hitting Macs as well as Window users.
Anti Virus websites such as Virus Bulletin warn not to download pirated copies of software. When you do you are placing your computer at risk.
I recall a college student returning software to J&R indicating the product did not work. J&R tests every piece of software that was returned and indicated to the student that he loaded a pirated copy of software that contained a virus and the virus infected his computer.
For Macintosh pirated copies of IWORK 09 and Adobe Photo Shop have been known to contain Malware. Zdnet in a nutshell indicated that 1000's of Mac computers could be infected. A "zombie" or botnet could turn your computer over to a remote user's bidding.
In any event, avoid pirated software, and especially "Torrents".
My personal rule is if you can not afford it, do not copy it.
Use only virus malware free software purchased from reliable sources, and downloads from Version Tracker, Apple.com (They make Window products also), Microsoft, Mactopia (MSN's Mac site), and other good sites.