Apparently, a new wave of Trojan spam e-mail attacks is being caused by up to 15 variants of the Bagle worm. The sheer number of variants is apparently making it difficult for anti-virus companies to update their security signatures to protect users from infection.
Some of the Trojans, being spread by a world network of "zombie" computers, are being used to install malicious remote monitoring software on users' machines, enabling criminals to monitor PC usage and steal personal details to commit fraud.
Apparently, these attacks are ongoing, and many of the minor variants are not detected by various security products. This presents a major problem for potentially effected systems - the number of which is staggering.