Anti-virus vendors report an increased chatter of virus activity on Microsoft Corp.s Microsoft Network messenger Sunday night through Monday.
In what appears to be a concentrated attack on users of the MSN instant messaging client, security experts warn that several new worms with unique replication techniques have been launched alongside mutants of the known Bropia virus family.
"We are regularly adding detection for new Bropia worm variants," F-Secure virus analyst Alexey Podrezov said in a notice.
Both Kelvir and Sumom, like the Bropia mutants, are capable of installing the Backdoor.Rbot Trojan horse, which gives an attacker remote access to a compromised system.
The Rbot Trojan can be controlled via IRC (Internet Relay Chat) to monitor networks and hijack sensitive information; scan a network of machines for unpatched security holes; or to launch denial-of-service attacks.
The Trojan can also be used to log keystrokes and send detailed information about the victim machine, including passwords, to the attacker.
Shane Coursen, senior technology consultant at Kaspersky Lab, said the increased instant messaging worm activity underscores the use of social engineering tactics to trick victims into executing a malicious file.
In the case of the Bropia variants, the worm author uses the lure of adult-oriented images (Paris Hiltons name is commonly associated with the worms) transmitted as hyperlinks in an IM session.
The worms all arrive with a .PIF (program information file) extension and, once a user clicks on the link, the computer becomes infected and in turn continues the propagation by sending the file to all found MSN Messenger contacts.