Just as some anti-virus vendors were saying the recent glut of viruses and worms was coming to an end, a new set of variants has appeared and restarted the almost daily update.

Following the arrival of Bagle.U late on Friday, yet another variant of Netsky - Q - and the Sober worm - E - have been released, were noticed Sunday, and definitions are being downloaded at start-up today.

In the past month, an apparent battle between rival virus writers has seen dozens of subtly different viruses and worms released on the Net. It started when one virus was designed to wipe out a competiting worm, creating a battle of words.

The virus writers then started putting text messages within the code of the viruses goading their rivals, and so to make a (usually petulant) response, it was necessary for another variant of the virus, taking advantage of a different security hole or human gullibility, to be released in order to spread to its intended audience.

And so on and so forth. And, ironically, press coverage of the whole situation has served only to make the situation worse but giving the virus writers an element of infamy.

At the end of last week, it had all gone quiet for a few days, but then the Bagle.U worm turned up and has sparked a knee-jerk reaction by those behind Sober and Netsky. Whether this in turn will create another cycle of worm variants, only time will tell, but one thing is clear - millions of Net users are growing increasingly frustrated with having to download new virus definitions every day just because a very small group of people are having a spat.