The US leads the world in numbers of Windows PCs that are part of botnets, reveals a report.

More than 2.2 million US PCs were found to be part of botnets, networks of hijacked home computers, in the first six months of 2010, it said.

Compiled by Microsoft, the research revealed that Brazil had the second highest level of infections at 550,000.

Infections were highest in South Korea where 14.6 out of every 1000 machines were found to be enrolled in botnets.

The 240-page Microsoft report took an in-depth look at botnets which, said Cliff Evans, head of security and identity at Microsoft UK, now sat at the centre of many cybercrime operations.

The research was undertaken, he said, to alert people to the growing danger from the malicious networks.

"Most people have this idea of a virus and how it used to announce itself," he said. "Few people know about botnets."

Full story: BBC News