(Reuters) – British mobile payments company Optimal Payments Plc said it was investigating allegations that personal data belonging to some of its customers had been compromised and was available in the public domain.

Optimal shares fell 11 percent to 309.5 pence, their sharpest fall in a day this year and lowest since Sept. 16.

The company said the allegations were that the data breaches had occurred at two of its units in 2012 or earlier.

The data consists of names and email addresses of customers and is available for purchase on the “dark web”, a source with knowledge of the hack told Reuters.

The dark web is an area of the Internet that can only be accessed through software that makes web browsing anonymous.

Optimal’s NETELLER and Moneybookers Ltd units had suffered data breaches as a result of cyber attacks in 2009 and 2010, but none of its customers lost any money as a result, the company said.

Optimal said it had informed the Information Commissioner and the Financial Conduct Authority (FCA) about the matter.

The company said it came to know about the allegations following media enquiries.

(Reporting By Mamidipudi Soumithri in Bengaluru; Editing by Anupama Dwivedi and Gopakumar Warrier)