More American personal computers have been taken over by hackers than in any other part of the world, a report has revealed.


Microsoft’s report said that in the first six months of 2010, more than 2.2 million U.S. PCs had been hijacked and now formed part of a botnet — virtual supercomputers with immense power, made up of millions of individual, hacked PCs.


Microsoft’s Cliff Evans, a digital security expert, said: “Most people have this idea of a virus and how it used to announce itself. Few people know about botnets.”


Criminals use botnets to send out spam and other so-called phishing scams and use botnets to launch attacks on individual websites. It has long been suspected that intelligence agencies of various countries, including China and Russia, routinely form botnets to attack Western countries’ banking and intelligence systems.


Owners of botnets also scour infected machines for information that they sell to other criminals on underground auction sites.

Microsoft said a botnet called Lethic sent out 56 percent of all botnet spam sent between March and June this year. Evans said, “It’s phenomenal, the amount of grip that thing has.”

Microsoft collected data from 600 million machines enrolled in its security update packages or that use its Essentials and Defender security software.