IT security experts have intercepted a previously undocumented Trojan virus with a novel payload that attempts to send spam SMS messages to mobile phones.

The Delf-HA Trojan horse (Troj/Delf-HA) infects PCs then contacts a Russian website to download instructions on which spam campaign to run. It can then plague mobile phone users by sending them unsolicited junk text messages, warned security firm Sophos.

Analysis of the Trojan's pathology shows that it sends spam SMS by using the 'Send a text message' facility found on the websites of several Russian mobile phone network providers.

"Mobile phone spam can not only be a nuisance, it can cost the phone owner money. In the past we have seen SMS spam campaigns designed to encourage recipients to ring an expensive phone number, or sign up for a costly chat-line service," said Graham Cluley, senior technology consultant for Sophos.

"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."

According to Sophos, only a small number of instances of the Trojan have been sighted so far. Further information about Troj/Delf-HA can be found here.