This danger is further compounded by the fact that security researchers have detected a hybrid threat from the Bagle.FN, which sends out the Mitglieder.FK Trojan from the computers it infects in order to increase its rate of propagation. This worm spreads by sending itself as a file attachment to the email addresses it finds on affected computers. Its main actions consist of leaving the computer unprotected and trying to download a file that generates emails to which it sends copies of Mitglieder.FK.
Even though new variants of Mitglieder have been released, their functions are very similar: Trojans that install themselves on computers and, in the case of the FK, FL and FN variants, try to download files from a remote website, can open the door to other threats. The main actions of the FN variant are to disable the antivirus protection installed on the computer, block access to web pages - mainly those belonging to IT security companies - and prevent users from modifying the registry, so that these actions cannot be undone.
"Without a doubt, the main trick of these variants is their extremely high rate of propagation, via both manual spamming and through the collaboration of the Bagle worms, which is not a new characteristic of this family," said Luis Corrons, director of PandaLabs.
"Among the companies hardest hit by these threats are those with email servers saturated with emails carrying these Trojans."