Anti-virus specialist Sophos has revealed the top ten viruses causing problems for businesses around the world.
Two new entries shot to the top of the charts, despite appearing only in the past two weeks.
Bagle shot to prominence on January 19 before falling dormant on January 28. MyDoom, programmed to launch a Denial of Service (DoS) attack on SCO's website from February 1, was even more rampant, reaching number one in less than a week.
MyDoom will fall dormant on February 12. These two viruses account for more than 40 per cent of reports to Sophos during January 2004.
The top ten viruses in January 2004 were:
W32/MyDoom-A; W32/Bagle-A; W32/Sober-C; W32/Dumaru-A; W32/Mimail-J; W32/Mimail-A; W32/Mimail-K; W32/Mimail-C; W32/Mimail-I; and W32/Klez-H.
"Both Bagle and MyDoom open up 'backdoors' on your PC. This means that once you are infected, attackers can take control of your computer remotely - this shows once again how much more important prevention is than cure," warns Paul Ducklin, head of technology at Sophos in Sydney.
Ducklin also warns about over-stating the threat.
"MyDoom has caused serious problems, mainly because of the large volume of email it has generated, but it also seems to have the dubious distinction of being the most-hyped virus in history," he said.
"We are already seeing statements that MyDoom has caused US$38 billion in damage, which somehow seems to beggar belief."
Sophos analysed and protected against 608 new viruses in January. The total number of viruses Sophos now protects against is 87,419.