A handful of people on the US official forums are reporting trojan issues when downloading patch 2.4.1.
As someone pointed out, Blizzard rarely release a patch that ends in .1, and there's the added "coincidence" that it's 2.4.1, note the date. Obviously Blizz would never worry their customers with a joke like this, but no one's sure what's going on right now. A Blizzard poster has confirmed that 2.4.1 is genuine, but people are still experiencing trojan warnings.
Worldofwar.net has been contacted by a number of forum users who assure them that the warning is a false positive, brought on by over-keen Anti Virus programs. If you do receive this warning during/just after downloading patch 2.4.1, rest assured you probably have nothing to worry about.