A security alert posted this morning by antivirus vendor Intego reveals that the company has discovered a new Trojan horse that is being carried by pirated copies of iWork '09 circulating on a number of torrent sites.

The Trojan, which Intego has classified as a "serious" risk and named OSX.Trojan.iServices.A, allows a malicious user to connect to an infected machine and perform various functions, as well as download additional software to the machine.

This software is installed as a startup item (in /System/Library/StartupItems/iWorkServices, a location reserved normally for Apple startup items), where it has read-write-execute permissions for root. The malicious software connects to a remote server over the Internet; this means that a malicious user will be alerted that this Trojan horse is installed on different Macs, and will have the ability to connect to them and perform various actions remotely. The Trojan horse may also download additional components to an infected Mac.

Intego reports that over 20,000 users had downloaded the package as of 6:00 AM Eastern time this morning, and an update to an entry posted on Intego's Mac Security Blog notes that the Trojan now appears to be actively downloading new code to infected machines and using them to carry out denial-of-service attacks on certain websites.

Update: Despite significant publicity surrounding this incident today, the infected iWork package remains active in the torrent community. In light of this continued activity, we have moved this report from Page 2 to our front page and are providing instructions for deactivating and removing the Trojan from infected systems.

1) (open Terminal.app)

2) sudo su (enter password)

3) rm -r /System/Library/StartupItems/iWorkServices

4) rm /private/tmp/.iWorkServices

5) rm /usr/bin/iWorkServices

6) rm -r /Library/Receipts/iWorkServices.pkg

7) killall -9 iWorkServices

OSX.Trojan.iServices.A appears to be the first significant OS X Trojan to advance beyond the proof-of-concept or pranking stage to engage in truly malicious behavior.

Update 2: MacScan has released a free utility to remove the Trojan from infected systems.