The US Federal Bureau of Investigation and UK’s Metropolitan Police are hunting a gang of six hackers based in the Ukraine who have hijacked 1.9m computers around the world, including machines at hundreds of large corporations and 77 government departments.

It is the largest network of hijacked computers – or botnet – to have been discovered. to date. It is at least four times larger than botnets that have been discovered in the past, which have tended to include 200,000 to 500,000 computers.