A security report by Microsoft claims more than 97 percent of all e-mails are spam, and that the global ratio of infected PCs is around 8.6 for every 1,000 uninfected machines. Another observation is that hackers are increasingly targeting flaws in Office and PDF documents.

Paul Woods, a senior analyst at security firm Message Labs, is surprised by Microsoft's findings. Woods says their own analysis shows that around 81 percent of all e-mail traffic is spam.

Microsoft said people should not panic about the high levels of unwanted e-mail.

Cliff Evans, head of security and privacy for Microsoft in the UK, told BBC News: "The good news is that the majority of that never hits your inbox although some will get through."

Ed Gibson, chief cyber security advisor at Microsoft, said the rise in spam was due to traditional organised crime figures moving away from exploiting software vulnerabilities and "targeting the weak link that is you and me".

"With higher capacity broadband and better OS (operating systems), and higher power computers it is easier now to send out billions of spams. Three or four years ago the capacity wasn't there."