French prosecutors have launched a money-laundering probe based on data stolen by an ex-employee of banking group HSBC, claiming it affected thousands of French clients with Swiss accounts. Prosecutor Eric de Montgolfier said the affair involved 8,231 French customers of HSBC who had accounts in Switzerland. Accounts held by around 7,000 Italians were also being examined, he said. A spokesman for HSBC said those numbers were “massively overstated”. HSBC said last month the data theft affected up to 24,000 Swiss client accounts, and yesterday said that estimate had not changed.