What  Edward Snowden is to mass surveillance, Hervé Falciani is becoming to private banking. In 2008 the now 41-year-old native of Monaco walked out of the Geneva branch of HSBC, where he had worked for three years, clutching five CD-ROMs containing data on thousands of account holders. The theft lobbed a bomb into Europe’s private-banking market, spawning raids and tax-evasion investigations continentwide. In the latest, this week, Belgian agents swooped on the homes of 20 HSBC clients, including some with ties to Antwerp diamond dealers.

Mr Falciani went on the run when the Swiss charged him with data theft. After moving to Spain he was imprisoned, but freed when a judge denied a Swiss extradition request. At one point, he claims, he was kidnapped by Mossad agents who wanted a peek at the clients’ names. He has now taken refuge in France, where the government has offered him protection in return for helping it 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 magnified the tumult in that country’s politics. Spain and France have fingered hundreds of high-level cheats and retrieved €350m ($610m) in back taxes. Mr Falciani maintains that his CDs provided support for an American probe into weak money-laundering controls at HSBC, which led to a $1.9 billion settlement. HSBC disputes this.

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 has been helping France’s tax authorities develop long-term anti-tax-evasion measures. And he recently became an adviser to a new Spanish political party, Partido X (which, ironically, tries to keep its members anonymous).

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 high-minded whistle-blower. He tried to sell the data at first, the bank contends, and started to work with prosecutors only when he was jailed in Spain. It claims he has data on only 15,000 clients (Mr Falciani says it is eight times that) and that the stolen files contain errors.

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

Banks and tax evasion: Hervé lifting, Economist, Oct. 19, 2013, at 79