Junk messages are following users and advertising dollars to social networking sites, according to an anti-spam researcher, who found that spam levels have tripled in recent months.

Cloudmark, which makes anti-spam platforms for service providers, said it tracked a 300 percent rise in junk messages at a major social network site it works with.

The company said all the major social networks have a spam problem, with between 15 percent and 30 percent of new accounts created for the purpose of sending advertising messages.

A spammer will typically create a social-network profile with a link to a porn or dating site and then use the profile to send friend invitations to large numbers of users, Cloudmark said.

Such invitations are more likely to be acted upon than emails received from unknown users, because the messages come from an authentic-looking profile and because social networks have large populations of technically naive users, according to Cloudmark.

Social network spam is not limited to friend invitations, but also includes social network tools such as pokes, chats, comments, bulletin board messages, blogs and application communications.

"The size and viral nature of social networks make Web 2.0 an attractive new target for spammers," said Cloudmark chief executive Hugh McCartney, in a statement.

He noted that junk emailers are not the only ones to recognise the advertising potential of social networks, with legitimate advertising revenues on social networks set to reach $2.2bn this year, according to a December 2007 report from eMarketer.

Earlier this week social networking site MySpace won a Los Angeles court judgement against Sanford "Spamford" Wallace and his partner Walter Rines for creating and hijacking accounts on the service to flood users with spam adverts for a range of goods.

The men sent 730,000 spam messages to MySpace users, some of which appeared to come from trusted contacts, rending asunder the whole concept that social networkers are in control of the contacts with whom they choose to associate.

Techworld's John Dunn contributed to this report.