Botnets want money, not to bring down the web
But it doesn't stop the possibility of groups with more anarchic plans from taking over bots for themselves.
Dr Steve Marsh, deputy director at the Office of Cyber Security in the Cabinet Office, said that the main focus of botnets would be to target and extort money from private companies, rather than bring down public sector networks.
He said that it was "in a sense not in their interest" to bring down infrastructure which is earning them money.
However, he warned: "Of course, there is the possibility some group with different intentions might try to exploit those mechanisms."
Marsh was speaking at a Home Affairs Committee meeting discussing EU policy on protecting Europe from cyber attack.
He claimed that in UK central government, the number of zombie machines' was "quite low" because of its network architecture.
"We have something called the Government Secure Internet (GSI)', which has quite stringent codes that departments have to sign up to before they connect," he said.
However, he couldn't guarantee that public networks were entirely free of compromised machines as some laptops and desktops wouldn't be connected through the GSI.
He added: "They may for business reasons have standalone machines that are connected directly to the internet, although we would encourage them to adopt the stringent security policies we have elsewhere."
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