An ingenious new Trojan is circulating that hijacks PCs and uses them to send SMS-based spam to mobile phones.

After a PC has been infected, the Delf-HA Trojan contacts a website for details on which spam campaign to run and then randomly generates a series of Russian mobile numbers beginning with the prefix +7921 or +7911. It uses the “send email” function of a number of Russian mobile network websites to actually deliver the mail sent from the infected machines.

That many of the numbers will not have been allocated to customers is of no consequence as enough real ones can be targeted randomly. The contents of the spam are believed to vary but one message shown to Techworld appeared to promote the download of mp3 music files from a named Russian website.

Although Delf-HA targets only Russian mobile networks, experts have warned that the same technique could be used to send spam to subscribers of networks in other countries.

"Now SMS spammers are taking a leaf out of the book of email spammers, and using unprotected innocent PCs to pass on their unwanted messages," said Graham Cluley of anti-virus vendor Sophos which uncovered the Trojan.

Spam is not a new phenomenon on mobiles but the volumes remain low compared to PC-based email. Delf-HA could signal a depressing turning point.

To date, most of the concern has centred around the possibility of viruses such as Cabir infecting mobiles themselves. Nokia also announced in the summer that it would offer anti-virus software for its 6670 smart phone.