The MyDoom worm has stormed to the top of the virus charts, accounting for more than a quarter of reported infections in January.

According to antivirus firm Sophos, MyDoom knocked another chart newcomer, the Bagle worm (with 16 per cent of infections), into second place.

Chris Belthoff, senior security analyst at Sophos, said in a statement: "Two new entrants dominate January's chart, yet both were first detected late in the month."

Even though the MyDoom worm only appeared on 26 January, it has accounted for one in four reports.

"The Bagle worm catapulted to the top very quickly," added Belthoff. "First detected halfway through the month, it shot up the chart in only a short amount of time."

Bagle's notoriety was short-lived, however, as it was designed to fall dormant on 28 January.

The top 10 viruses in January 2004, according to Sophos, were as follows:

1. W32/MyDoom.A - 25.1 per cent (New entry)

2. W32/Bagle.A - 16.3 per cent (New entry)

3. W32/Sober.C - 9.9 per cent

4. W32/Dumaru.A - 5.3 per cent

5. W32/Mimail.J - 3.1 per cent

6. W32/Mimail.A - 2.7 per cent

7. W32/Mimail.K - 2.6 per cent

8. W32/Mimail.C - 2.2 per cent

9. W32/Mimail.I - 1.0 per cent

10.W32/Klez.H - 0.8 per cent (24 months in chart)

As well as identifying 608 previously undiscovered viruses in January, Sophos reported that a long-running Hotmail email chain letter hoax continued to top the chart of most widespread hoaxes.

"The Hotmail hoax refuses to shift from top place in the chart," said Belthoff.

"Hoaxes and chain letters clog email servers and waste valuable bandwidth; all companies are advised to implement an anti-hoax policy."