- The number of malicious programs found online has reached an unprecedented high, say security firms.
Reports vary but some estimates suggest there were five times as many variants of malicious programs in circulation in 2007 compared to 2006.
Security company Panda Software said it was getting more than 3,000 novel samples of so called malware every day.
Criminals pump out variants to fool anti-virus programs that work, in part, by spotting common characteristics.
Security software testing organisation AV Test reported that it saw 5.49 million unique samples of malicious software in 2007 - five times more than the 972,606 it saw in 2006.
AV Test reached its total by analysing malicious programs and generating a digital fingerprint for each unique sample.
The organisation said the different ways malware can be packaged will mean some duplication in its figures, but the broad trend showed a steep rise.
The organisation uses the samples to test security programs to see how many they can spot and stop.
Panda Software said the number of malicious samples it received in 2007 was up ten fold on 2006. In a statement it said the rise represented a "malware epidemic".