Hundreds of thousands of computers in Asia and the Middle East have had their data wiped by a malicious program known as the Chernobyl virus.

It was timed to strike on Monday, the 13th anniversary of the nuclear reactor disaster, and computer network managers in the regions have since been counting the cost.

While Chernobyl, a variant of the CIH virus, had a damaging impact in some parts of the world, the US and Europe seem to have largely escaped its effects.

Chernobyl around since June

CIH was discovered as long ago as last June in Taiwan. But despite warnings about its deadly effects on Windows 95 or 98 machines from anti-virus software companies since then, it still appears to have wreaked havoc in certain countries.

In the West, companies had protected their computers with anti-virus programs that killed it, but in Asia and the Middle East the same precautions had been ignored in many cases.

Chernobyl also spreads through pirated software, which is rife in these parts of the world. The virus can delete most of the data stored on computers and can even wipe out the BIOS - the basic instructions that tell the computer to start.

Asian countries worst-hit

Countries in Asia appear to have been affected the worst by the virus:

• China: The state-run media reported that more than 100,000 computers had been affected across China.
• South Korea: Government officials apologised for not taking more urgent action and estimated that 250,000 PCs were attacked and $250m in damage had been caused.
• India: More than 30,000 computers had crashed, said experts and officials. Major industries, banks and other financial institutions had been badly hit.

Middle East suffers 'catastrophe'

Middle East and Gulf countries were also badly hit:

• Israel: Israeli data recovery experts said there had been a catastrophe with thousands of computers affected, including those of a major financial institution, an intelligence organisation and a large Internet Service Provider.
• Egypt: Companies in Cairo sent workers home as their systems were paralysed by the virus. "It's a disaster," said one civil engineering firm.
• The Gulf: Industry in the United Arab Emirates estimated that 5-10% of computers had been affected, while there were reports from Qatar of the infection reaching "epidemic" proportions.
• Turkey: Banks, police departments, an army school, state television and government offices were hit.