A 41-YEAR-OLD native of Monaco increasingly looks to be to banking what Edward Snowden is to American surveillance. In 2008 Hervé Falciani walked out of the Geneva branch of HSBC where he’d worked for three years, clutching five CD-Roms containing data on tens of thousands of account holders. The theft has lobbed a bomb into Europe’s private-banking market, spawning raids and tax-evasion investigations across the continent. In the latest, 90 Belgian agents swooped on the homes of two dozen HSBC clients this week, including several diamond dealers in Antwerp.

Mr Falciani went on the run when the Swiss charged him with data theft. After moving to Spain he was jailed, but freed after a judge denied a Swiss extradition request. At one point, he claims, he was kidnapped by Mossad agents who wanted a peek at the client names. He has now taken refuge in France, where the government has offered him protection in return for assisting in its hunt for tax dodgers.



Several countries have used the data to bring cases against suspected evaders. Revelations that dozens of Greek public figures hid money offshore have shaken that country’s politics. Spain and France have fingered hundreds of high-level cheats and retrieved €350m in back taxes. Mr Falciani has claimed that the CDs provided crucial support for an American probe into the failure of money-laundering controls at HSBC, which led to a $1.9 billion settlement.



Mr Falciani has said he still fears for his safety, despite round-the-clock protection from three armed guards provided by the French. At least he is not short of work. He is acting as a consultant to France’s tax authorities on developing long-term anti-tax evasion measures. And he recently became an adviser to a new Spanish political party, Partido X (which, ironically, prizes its members' anonymity).



He insists his motives have always been pure: to repel Switzerland’s “attack” on other countries’ tax laws and exchequers. HSBC says he is no whistleblower. He tried to sell the data at first, the bank contends, and only started to work with prosecutors when he was jailed in Spain. It says he took information on only 15,000 clients (Mr Falciani claims it was many times that number) and that a portion the bank has seen contains errors.



Regardless, many more tax-shy Europeans have reason to sleep fitfully. Other countries are said to want a look at the pilfered data, much of which is apparently yet to be decrypted. When Mr Falciani first made the rounds with his discs, governments showed little interest. The fiscal strains produced by the euro crisis have changed all that.