Shares in Optimal Payments fell seven per cent after the London-listed firm confirmed that customer data taken in data breaches has made its way into the public domain.
In a statement, the mobile payments company says there are allegations that two of its units, Neteller and Moneybookers, suffered data breaches in 2012 or earlier.
A "small amount" of customer data - understood to be names and email addresses - has got out into the open and appears to be for sale on the dark web. More information could be out there.
Shares in Optimal fell by as much as 11% during the day before recovering slightly to 323 pence per share, a seven per cent drop.