The Trojan software found last week in unauthorized versions of Apple's iWork 09 productivity suite has been spotted lingering around Adobe Photoshop CS4.

On Monday, Intego, the Mac-oriented security software maker that sounded the initial alarm about the iWorkServices Trojan, said that it has discovered a variant of the Trojan.

"This new Trojan horse, OSX.Trojan.iServices.B, like the previous version, is found in pirated software distributed via BitTorrent trackers and other sites containing links to pirated software," the company said in an online post. "OSX.Trojan.iServices.B Trojan horse is found bundled with copies of Adobe Photoshop CS4 for Mac. The actual Photoshop installer is clean, but the Trojan horse is found in a crack application that serializes the program."

Users who download Photoshop CS4 from a peer-to-peer network would typically run the accompanying crack application to make Photoshop work without an authorized serial number. But the crack application in this case installs a back door with a randomized name in the /var/tmp/ directory, according to Intego. It then asks for an administrator password to operate the back door with root privileges.

At this point, the victim's computer, given an Internet connection, can be operated covertly by the remote attacker.

Intego claims that as of 6 a.m. EST on Monday, about 5,000 people had downloaded the infected Adobe software.

On Friday, Arbor Networks warned that the iWorkServices Trojan hijacks victims' computers and forces them to serve in a P2P botnet. "The bot software itself appears to be a Kadima-related P2P protocol with the expected commands to manage the peer list, but also to provide a remote shell, download and run arbitrary code, and to give full access to the box," said Arbor Networks senior security researcher Jose Nazario in a blog post.