From late May through June, Commtouch Labs noted a sharp rise in the number of new viruses being circulated via email that were not caught by the major anti-virus engines. A new Malware Report released by the company details several outbreaks whose wide distribution caused malware numbers to temporarily and exponentially increase from the rather consistently low numbers we have seen during the past 18 months.
One explanation for the dramatic rise is the appearance of aggressive new variants of several different Trojans. With each new variant, there is a period of time during which anti-virus companies recognize it and then develop new signatures to protect their customers. The companies have tried blocking new variants with a dedicated signature per variant. This method proved inefficient, so security vendors have begun to develop generic signatures to block all variants of the same malware family. As demonstrated by this massive growth, the generic signatures have not proven to work against the recent variants.
Download the full Malware Report here.