The cyber wargame, which was organised by the Bank of England and designed by a team from Credit Suisse, was called Waking Shark II and challenged participants to deal with a mock-up of a cyber attack as if it were happening in real-time.
Representatives from organisations including Barclays, Bank of America, Goldman Sachs, HSBC, London Stock Exchange and Royal Bank of Scotland are understood to have taken part in the exercise.
The event was overseen by officials from the Bank of England, the Treasury and Financial Conduct Authority.
The test took place in a single room of The Plaisterers' Hall, with people from various organisations interacting as the scenario unfolded.
The Bank of England said it would publish the results of the war game early next year.