EU tests Europe bank Web services for vulnerability to hacking

* EU hackathon to expose vulnerabilities

* EU Commission writing strategy to tackle attacks

By Claire Davenport

BRUSSELS, Oct 4 (Reuters) - European Commission computer experts orchestrated attacks on mock Internet sites in Europe's largest ever cyber-security exercise on Thursday to uncover weaknesses in the computer systems of major European banks.

The test was organised by European Union countries with the backing of the Commission, which is preparing to draft new legislation on cyber security.

The exercise used the same type of assault - 1,200 separate attacks including over 30,000 emails - that hit JPMorgan Chase

and Wells Fargo last week, designed to force them to shut down service.

The number and names of the companies involved in the exercise were not disclosed, although they included major banks in London and Frankfurt. Altogether 400 computer specialists at these companies will be tested for their reactions to the assault, the Commission said.

Security experts warn that companies could experience increasing losses from hackers as cyber attacks become more frequent. In 2011 there were four times more attacks than the previous year, and each time the financial loss increased.

In June, Britain's secret service MI5 said a major listed company lost 800 million pounds ($1.3 billion) in just one attack. The company's name was kept secret.

The European Network and Information Security Agency said it would present the initial results from the EU-wide tests in the coming days. The attacks were conducted by experts working for the Commission's Joint Research Centre.

The European Commission will publish a strategy to strengthen cyber security by the end of the year.

($1 = 0.6222 British pounds)

(Reporting by Claire Davenport; editing by Jane Baird)