Police, private security experts and internet service providers said on Wednesday they had shut down the Mariposa botnet, one of the largest networks of hacked personal computers discovered.

It had siphoned off financial and other information from inside half of the largest 1,000 US companies.

Computers using about 12.7m internet addresses in 190 countries were compromised, although some machines might have been using multiple addresses.

The Conficker network, which was discovered last year and blocked from further expansion by a co-ordinated international effort, was estimated to have had between 1m and 10m “hosts”.

Such collections of infiltrated PCs are the main tool of criminal gangs that pilfer banking credentials for fraudulent withdrawals. Other groups harvest all they can from the machines, looking for valuable intellectual property, as in the recent attacks conducted from China against Google, Symantec and other technology groups.

There are thousands of such networks of PCs that appear normal but are being operated remotely, known as robots or bots. Efforts by law enforcement agencies to take the collections, called botnets, offline occasionally succeed.