According to Mac security software company Intego, which has put out the alert, OSX.Trojan.iServices.A allows users to install a fully-working copy of iWork 09 as normal, but only at the price of letting malware bury into OS X using a rogue install add-on.
As with a lot of PC Trojans, the immediate purpose of the software is simply to compromise the OS X system comprehensively enough to allow for the downloading of further malware from a remote host, another way of saying that the user could be opening themselves up to more or less anything the writers fancy putting on the system.
According to Intego, this is no theoretical infection that will affect only a handful of people, having been downloaded at least 20,000 times using the BitTottent file sharing system in recent days.
Apple's iWork software, which would normally set the user back around £70 ($79), is an all-purpose program that includes document, spreadsheet and presentation features. The latest version that is being used as a lure on BitTorrent distributions sites, will be sought after by users of pirated software having been released only weeks ago.
The company stands to benefit from the alert of course - it is currently virtually the only Mac-only software security outfit. The big-name anti-virus products sold for Macs tend to be spin-offs from much more lucrative PC protection programs.
"Intego VirusBarrier X4 and X5 with virus definitions dated January 22, 2009 or later protect against this Trojan horse," the company said in a release.
The number of Trojans affecting Mac users is on a modest upward curve, helped the company said during a recent and separate Mac Trojan outbreak, by the tendency of some Apple users to see their computers as above Windows-like security woes. The number of companies that actively track malware targeting Apple users is also proportionately smaller than for Windows PCs.
This story, "Mac BitTorrent Users Warned of Trojan" was originally published by Techworld.com.