To the untrained eye Mytob and Zotob can appear quite different: one group of viruses travels via email, the other primarily by exploiting a Microsoft security hole.

If he had been scanning his email for viruses he would never have received the message from the Sober worm. If jailed he'll have plenty of time to reflect on whether he should have believed everything that was sent to him via e-mail.

Trojans are different from viruses because they can lurk in PCs without anyone noticing and can spy on the computer user's activities then send this information back anywhere in the world.

There are a tiny number of mobile-phone viruses compared to the threat on the Windows platform.

It appears that whoever wrote Zotob had access to the Mytob source code, ripped out the email-spreading section, and plugged in the Microsoft exploit. It's possible that several people have access to the Mytob source code - so it may not be the last we see of this Internet scourge.

It appears whoever wrote Zotob had access to the Mytob source code, ripped out the email-spreading section and plugged in the Microsoft exploit.