The program, a Trojan horse known as Troj/Delf-HA, takes control of any computer whose user runs the malicious software, antivirus company Sophos said. It then uses Russian text-messaging services to send a Short Message Service (SMS) file to mobile phone users at random.
"Mobile-phone spam is a huge nuisance and can run up an expensive phone bill for owners," Gregg Mastoras, senior security analyst at Sophos, said in a statement posted on Monday. "SMS spammers are now using unprotected, innocent PCs to pass on their unwanted messages."
The Delf Trojan horse does not aim to enter and infect the mobile phone itself, unlike previous nuisances, such as Cabir. Instead, it compromises PCs and sends out messages from there.
Four years ago, a virus known as Timfonica used PCs to send a deluge of SMS messages to mobile phone users in Spain. Previous SMS spam campaigns have attempted to get mobile phone users to call a pay-per-minute number or sign up for costly hotline services, Mastoras stated.
Some experts believe that mobile-phone spam could quickly become as large a problem as Internet spam.
In August, the Federal Communications Commission voted to restrict unsolicited messages to mobile phone users unless the recipients had agreed to receive the messages. However, the commission did not extend the ruling to unsolicited text messages sent through mechanisms like SMS, which could make the decision ineffectual.
The Delf Trojan horse downloads the spam message that it intends to send from a Russian Web site. Unlike a virus, the program does not automatically try to spread to other computers. It relies on the attacker to send out the malicious software to potential victim PCs.
People can help guard their systems against Trojan horses by only clicking on e-mail attachments that they trust.
