* Exercise involved "fake foreign government attack"-source
* Also involved "denial of service attack" - source
* Event dubbed "Waking Shark II"
* Bank of England has told banks to strengthen defences
LONDON, Nov 12 (Reuters) - A cyber attack on financial markets played out in one of London's historic halls on Tuesday in a "war game" simulation designed to test the City's defences against online saboteurs.
About 100 bankers, regulators, government officials and market infrastructure providers gathered to take part in an exercise dubbed "Waking Shark II" at Plaisterers' Hall, the historic home of the plastering industry and more normally a venue for banquets and conferences.
Regulators and companies are growing increasingly concerned about the threat of cyber crime to the banking system, including the impact of coordinated online assaults or hacking attacks on specific lenders. The Bank of England has told banks to strengthen their defences against cyber attacks.
One unidentified London-listed company incurred losses of 800 million pounds ($1.3 billion) in a cyber attack several years ago, according to British security services.
Tuesday's five and a half hour event ran from 1200 GMT and involved simulations designed to test how well banks and other market players communicate and coordinate with authorities and each other, sources told Reuters.
An industry source who attended said one of the simulations featured a cyber attack by a fake foreign government and a denial-of-service (DOS) attack, which makes network resources unavailable to users.
The source described the test as a "productive exercise" which left participants better equipped to deal with a real-life attack.
The event, one of the largest of its kind in the world, follows a similar large-scale simulation in New York this year dubbed "Quantum Dawn 2" and comes amid heightened fears over the threat from hacking and cyber attacks.
"This is a good opportunity to iron out any flaws now before our cyber defences are tested in anger," said Stephen Bonner, a partner in KPMG's Information Protection & Business Resilience team.
Richard Horne, a partner at PricewaterhouseCoopers who specialises in cyber security, said the exercise was useful but the real challenge lay in co-ordinating across the industry to make sure a crisis scenario is never reached.
"It will take a lot of detailed technical work and testing, coordinated across the industry, to really understand all the interdependencies and develop meaningful containment and recovery plans," Horne said.
The investment banking industry itself played a key role in co-ordinating the exercise, along with the Bank of England, the Treasury and the Financial Conduct Authority (FCA) and follows a similar exercise two years ago, the sources said.
Institutions involved in this year's test included Barclays , BNP Paribas, Bank of America, CHAPS, Commerzbank, Credit Suisse, Deutsche Bank , Euroclear, Goldman Sachs, HSBC, JP Morgan, LCH Clearnet, London Stock Exchange, Morgan Stanley, Nomura, Royal Bank of Scotland , SocGen, SWIFT and UBS, according to a source familiar with the matter.