A helpful virus called the "cheese worm" is making its way around the Web checking computers for weaknesses and fixing problems as it finds them.

The worm targets computers running Linux.

Although the most common viruses attack Microsoft Windows, the increasingly popular Linux software is fast becoming a favourite target for virus writers.

This year, four viruses, the Ramen, Lion, Adore and Sadmind/IIS worms, were detected, attacking this software.

The cheese worm attempts to repair some of the damage done by the Lion worm.

Comments inside the code for the worm spell out its friendly intent. One reads: "This code was not written with malicious intent". The cheese worm claims to have been created: "to stop pesky haqz0rs (hackers) messing up your box even worse than it is already".

But in spite of these friendly words, the cheese worm hasn't been welcomed. That's because anti-virus companies say any software making unauthorized changes to a computer is potentially dangerous.