MADRID: Spanish police and Europol, the European Union's police coordination agency, have busted a global cybercrime operation that infected millions of computers, a source in the investigation told AFP.

The network used malicious software to block computers and send a message claiming to be from police demanding the user pay a fine for allegedly accessing child pornography sites, the source said.

The ring operated several small cells around the world and was able to collect large amounts of money with the scheme, the source said.

"One of these cells earned over one million euros," around $1.3 million, the source said.

Several people were arrested but the final number could not yet be revealed because the operation remained open.

Europol director Rob Wainwright and Spain's secretary of state for security, Francisco Martinez, were due to give further details at a press conference later on Tuesday in Madrid.

Last month Europol opened a new cybercrime unit at its headquarters in The Hague aimed at fighting online offenses such as bank fraud and peddling images of the sexual abuse of minors.