Computer experts race against the clock to thwart Citadel virus in Hong Kong

Computer experts in Hong Kong are racing against time to stop a virus that could put "a considerable number" of computers under the control of hackers.

The emergency operation follows an internationally co-ordinated crackdown, in which Hong Kong played a part, on what is deemed "one of the world's biggest cybercrime rings". It is believed to have stolen more than US$500 million from bank accounts around the world over the past 18 months.

Microsoft, which has led the crackdown with the FBI in conjunction with authorities in more than 80 countries, said its digital crimes unit had successfully taken down at least 1,000 of an estimated 1,400 malicious computer networks called the Citadel Botnets.

Citadel monitors keystrokes on infected computers and sends information such as account names and passwords to hackers, so cybercriminals can use stolen passwords to steal money from online bank accounts.

As many as five million computers in 90 countries have reportedly been infected, with bank accounts at dozens of financial institutions - including American Express, Bank of America, Citigroup, eBay's PayPal, and HSBC - affected, according to Microsoft.

Hong Kong is one of the places with the most infections.

Citadel is programmed so it will not attack computers or financial institutions in Ukraine or Russia, probably because the creators operate in those countries and want to avoid provoking law enforcement officials there, Microsoft said.