LONDON - More than 97 percent of all emails sent in the world are unwanted spam, says a Microsoft security report.

According to the report, e-mails are dominated by spam adverts for drugs, and general product pitches.

The global ratio of infected machines was 8.6 for every 1,000 uninfected machines, the study found.

It also found that Office document attachments and PDF files were increasingly being targeted by hackers.

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, blamed the rise in spam 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," he said.

Paul Wood, senior analyst at e-mail security firm Message Labs, said he was amazed the Microsoft figure for unwanted e-mail was so high.

"Our own analysis shows that around 81 percent of e-mail traffic we were processing was identified as spam and unwanted," he said. (ANI)