The latest threat report from security firm McAfee has found that spam, malware and other web-based threats have reached record levels.

Web-based threats are currently the most popular vector, according to the Third Quarter 2009 McAfee Threats Report (PDF), but McAfee warned that enterprises are also facing a rise in extortion attempts from criminals using the threat of denial-of-service (DoS) attacks.

Spam has reached record levels, the report said, attaining 92 per cent of all email during the three-month period and representing a rise of 24 per cent compared to the same period last year.

Web attacks are now one of the most dangerous and sophisticated vectors used by criminals, the report found. Attacks can come from malicious web pages, redirects, hijacked legitimate sites, phishing emails and social networks.

"Malware authors take advantage of news stories like the death of celebrities and natural disasters to hide their malicious intentions," McAfee said.

"For example, some results returned when users searched for information on Patrick Swayze's funeral led to a 'scareware' page which told users that their PCs were infected with multiple viruses."

Around 13 million new compromised PCs were added to global botnets during the quarter, representing a modest fall of one million against the previous three months. McAfee estimates that 148,000 new 'zombie PCs' have been added every day in 2009. Most zombies are created in the US, at just over 13 per cent, while the UK is ninth on the list with just under three per cent.

The use of DoS attacks has also risen during the period. McAfee highlighted the cases of four Australian sports betting firms' web sites being taken down during key events, costing them millions in lost revenue.

The security firm also logged a rise in political attacks. "We know of many distributed DoS attacks used by individuals or groups to silence an opposing political voice or to retaliate against government opinions or rules," said the report.

"Examples include the politically motivated attack to silence a Georgian activist, and the threats against the Australian government."