An unnamed virus has been blamed for an embarrassing suspension of the Russian stock exchange last Thursday.

Details of the virus have been hard to come by – UK sources confirmed that the culprit is not yet known in security circles – but the downtime lasted an hour and affected the three main exchanges run by the Russian Trading System (RTS).

RTS described the attack as being virus-related, but then appeared to point to a scenario more attributable to a straight denial-of-service (DoS) attack in its public statements.

"The infected computer started generating huge volumes of parasitic traffic, which overloaded the RTS' support routers. The result was that normal traffic, data going into and out of the trading system, was not processed," RTS vice president said Dmitry Shatsky was quoted by sources as saying.

The lack of clarification from RTS has fuelled speculation that the attack was made through a compromised host, which was then used to mount an traffic-based assault on company routers.