Sydney - International hackers are holding Australian businesses to ransom by hijacking their computer systems, police warned on Sunday.
Fraud squad detectives said tens of thousands of Australian businesses have been targeted by the international cyber gangsters.
Detective Inspector Bruce van der Graaf told The Sun-Herald newspaper that crime gangs hijack their victims' computers and demand thousands of dollars before they can be used again.
The internet criminals hack their way into a firm's computers and deliver a virus to encrypt all data.
They tell the firm via email they will only release the computers once the firm sends money via hard-to-trace cash transfer systems such as Western Union.
Another scam is to tell people that police discovered child abuse material on their computer and will remove it after payment of a fine.
The detective said many firms were paying the ransom rather than lose days or weeks of trade.
Some companies including a medical centre and a school refused to pay up and lost all their computer records.
Emails from the cyber criminals often come in both English and Russian, leading police to believe they are based in eastern Europe. - Sapa-dpa