The numbers of viruses, worms, Trojans and other malicious programs aimed at PC users has now surpassed 100,000.
Many malicious programs target your personal data
According to security firm McAfee, a variant of the Sdbot bug has the honour of being the 100,000th security threat.
This bug tries to install backdoors on PCs to turn them into spam relays, spread viruses or steal personal data.
McAfee said it had seen big increases in the number of viruses produced as creators of malicious programs try to outwit security software.
In its definition of security threats, McAfee includes viruses, Trojans and worms as well as the adware and spyware programs that find their way on to home PCs.
Vincent Gullotto, spokesman for McAfee, said adware and spyware fall into a category it calls "Potentially Unwanted Programs" because many people fall victim to such programs without knowing they are being installed.
Adware delivers pop-up adverts inside and outside net browsing sessions while spyware keeps an eye on the sites you visit or what you do on your computer.
Mr Gullotto said McAfee had seen the creation of 22,000 novel security threats in 2003, most of them affecting Microsoft Windows, and 2004 looked like surpassing this figure.
At the moment McAfee, and many other anti-virus firms, are seeing 25-50 new viruses or variants of old ones every day.
Mr Gullotto said so many versions of some viruses were being produced in a bid to outsmart the anti-virus software that many people have installed.
Sven Jaschan, the German teenager charged with creating the Sasser worm, is also suspected of being behind the Netsky virus.
If this is true, it means that Mr Jaschan alone was responsible for 70% of the virus activity in the first six months of 2004.
But, said Mr Gullotto, the news about the numbers of viruses and other security threats in circulation is not all bad.
Many virus writers are in it for the money
He said the number of security threats found in the wild was staying broadly constant at around 1,300 items.
"The more of it we see, the better we will probably get at stopping the threats," he told BBC News Online.
One of the biggest changes that McAfee had seen over the past year was the growth of security threats crafted by people who want to make money from malicious programs.
Many people are creating viruses that set up networks of remotely controlled computers and are then renting out the networks to spammers, other virus writers or people that want to launch denial-of-service attacks.
Some simply wanted to create a network of remotely controlled computers so they can grab personal information such as credit card numbers and banking information to steal money.
According to a recent study by another anti-virus firm, Symantec, more than 30,000 PCs per day are being recruited to serve as zombie machines.
One type of virus that was on the wane, said Mr Gullotto, was the mass-mailing bug.
"There have not been as many high-profile attacks and the reason for that is mass-mailers are not as successful as they have been," he said.
Efforts in the corporate sector to install anti-virus software and spot viruses that try to trick people into opening them now limit the effectiveness of such viruses, he said.
"Now," said Mr Gullotto, "most of our submissions come from home users."
"Home users are getting better at protecting themselves," he said, "but I do not think they are anywhere close to where the corporates are."