The London Stock Exchange's new open source trading system may have been hacked last year, according to a report.
The alleged attack came as the LSE began the switch over to the Linux-based systems, according to the dates referred to in the Times newspaper.
The continued threat of cyber attack has resulted in the LSE keeping a close dialogue with British security services, which this year branded cyber attacks as one of the biggest threats to the country.
There were major problems on the exchange on 24 August, when stock prices of five large companies collapsed. Most notably, BT shares lost £968 million, and the LSE was forced to halt trading for the day. The exchange blamed an incorrectly entered price on a large number of stock orders.
But the trading system was also thrown offline last November in what the LSE called "suspicious circumstances". So far, the official explanation is human error, but it is understood that the police have been drawn into investigations.
Unlike US exchanges, the LSE platform is not based on the internet, and therefore is less vulnerable to general cyber attacks. However, cyber attacks on exchanges are becoming more advanced, according to security experts, and this poses new threats.
The LSE declined to comment on the events, ongoing investigations or possible motives for any attacks.
The new Linux system, based in a C++ environment, is already live on the LSE's Turquoise, or anonymous, trading venue.
As the concern and speculation deepens around the LSE outages, the exchange is due to switch on the new Linux systems on its main exchange in two weeks' time, with dress rehearsals over the coming two weekends. The system replaces a Microsoft .Net architecture.