Kaspersky Lab has published a new article describing how botnets are created and operated.

According to the company, botnets have evolved over the last ten years into one of the most serious information security threats.

Kaspersky claims that botnets have "vast computing power" and can be an "effective tool" for making money illegally.

A botnet is a network of computers which are infected with malicious programs that cybercriminals can remotely control.

Kaspersky says that sending spam is the most common use for botnets and experts estimate that over 80 per cent of spam is sent from zombie computers. According to the company's data, an average spammer makes up to $100,000 a year.

Another popular attack method is to send a stream of requests from hundreds of bot-infected machines, overloading the server and demanding payment from the server's owner in return for stopping the attack.

Kaspersky says that cybercriminals can commit cybercrimes using zombie computers such as hacking websites or transferring stolen money.

TechWorld.com recently reported that the Srizbi botnet now accounts for up to 50 per cent of the spam being filtered by security company Marshal.

It is estimated that the botnet has compromised 300,000 PCs and is now sending 60 billion spam emails per day on watches, pens and male enlargement pills.