Stock exchanges in the UK and US have called in security services to help fend off cyber-attacks, according to the Times newspaper.
In November the London Stock Exchange hinted that foul play may have been involved in an outage at its Turquoise trading platform.
It has also faced real world attacks, calling in the Cabinet Office after uncovering a terrorist plot on its headquarters behind St Paul's Cathedral last year.
Meanwhile, the paper says US officials are investigating a cyber-attack on an American exchange, tracing it to Russia, with "unusual" trading patterns at New York and Chicago platforms also under scrutiny.
The Times also casts doubts on the official verdicts on the 6 May flash crash, which saw the Dow Jones Industrial Average shipped more than 1000 points in minutes, and a similar problem in London in August.
A joint SEC/CFTC report largely laid the blame for the Dow plunge on a massive sale of e-mini futures by asset management house Waddell & Reed after a technical blip triggered a rash of selling.
However, the Times suggests security services looking into the event have not ruled out a cyber-attack by groups seeking to wipe billions off the value of companies, panicking markets and destabilising the West's financial system.
The LSE is less susceptible to these threats because, unlike its New York contemporaries, its systems are not Internet-based. However the most recent outages at the Exchange have coincided with the switch-over to the new Millennium trading platform, leading to suspicions about the stability of the Linux-based system and its susceptibility to hacking.
Earlier this month the bourse backed off claims of "suspicious behaviour", concluding only that human error was to blame but the Times, citing "well-placed intelligence sources" says the LSE has still been seeking to identify the "source and motive".
The November breakdown was severe enough to force the Exchange to suspend the planned migration of the main cash equities market to Millennium by three months, with the switch-over now set for two weeks time.