Trading on the London stock market was thrown into confusion after technical problems resulted in misleading information being published.
Data problems have disrupted trading
In a highly unusual move, trading on the London Stock Exchange (LSE) was extended to 1800 GMT after terminals in the City displayed incorrect prices.
These showed the benchmark FTSE 100 closing up on Wednesday, even though it was sharply down for most of the day.
The LSE blamed the disruption on problems with "data dissemination".
This resulted in incorrect figures for the FTSE 100 and for the performance of some individual company shares being displayed.
The LSE said it had experienced problems with "data feeds" at 1600 GMT, about half an hour before the market's normal close.
These "connectivity problems" had affected price information which providers such as Reuters and Bloomberg sell on to traders and other City professionals.
Revised figures after the extra's hour trading showed the FTSE 100 down 54.8 points at 6420.1, with shares of leading banks and mortgage lenders under continuing pressure.
The disruption to trading will be a serious embarrassment for the LSE, one of the world's largest stock market operators.
It recently acquired Italy's Borsa Italiana for £1.6bn, a deal which the LSE said would create Europe's largest market for trading shares.