April was an unusual month according to <A HREF="http://www.viruslist.com/">Kaspersky's Senior Virus Analyst Alexander Gostev,</A> with variant Dlena.cb not only making the rankings for the very first time, but also topping the charts in its debut appearance. Dlena.cb is a program from a large family of Trojans with approximately 90 variants, and in over a year of being detected, there's never been a single user complaint about any program from this family--until now. And although Dlena.cb is so far a typical Trojan proxy which can be used to send spam, it may cause serious problems in the near future.

NetSky.t also made an unexpected return to the top of the email charts. In the three years since NetSky.t appeared, its highest ranking ever was fourth place in February 2006. It subsequently disappeared from the rankings and later returned to lurk close to the top of the table, and this month has pushed aside all the new generations of worms, taking first place by storm.