Faced with a threat that already costs billions in lost sales and damaged reputations, global business is fighting back against the hackers.

In an effort to help law enforcement agencies identify authors of viruses and bring them to justice, Microsoft has set up something called the Microsoft Antivirus Reward Program.

It has seeded the program with $5m - cash to be used as a monetary inducement to informants willing to spill the beans on virus creators.

As a sign of its seriousness, Microsoft has offered a quarter of a million dollars for information leading to the arrest and conviction of those responsible for designing the MSBlastA worm (also known as Blaster). A similar amount awaits anyone who can identify those behind Sobig.

Companies are taking virus authors more seriously because the nature of the threat has changed.

The common stereotype of a spotty teenager hacking into the US Department of Defence computer for a spot of thermo-nuclear war just out of curiosity is no more.

Many virus creators are members of organised gangs who write destructive programmes to impress their peers. They often give themselves catchy names, such as 29A, YAM (Youth Against McAfee), Metaphase, and Phalcon Skism (Smart Kids Into Sick Methods).

According to Graham Cluley, of anti-virus company Sophos: "The gangs give the adolescents a sense of belonging and help raise their esteem."

Some of these groups even try to justify their dubious hobby by claiming viruses should be looked upon as an art form and a type of self-expression worthy of approbation. Anyone who has ever fallen victim to one of their viruses would take a different view.

Thanks to the popularity of virus creation, writing a malicious programme is no longer a great skill.

If you know where to look among the seedier parts of the Internet - sites that deal in "Warez", the illegally-hacked commercial programmes made available for download - it is a simple matter to obtain a virus toolkit.

Armed with this software, even someone with moderate computing knowledge could create a virus inside a few days.

The other type of hacker is just as likely to be motivated by greed as innocent curiosity.

This new breed are nothing more than a bunch of electronic extortionists who threaten virus attacks unless they are paid.

If bringing down a network can cripple a company, the temptation to pay up must sometimes be overwhelming.

No wonder Microsoft is prepared to offer the one inducement everyone knows can crack these hackers - good old fashioned money.