PARIS — Hervé Falciani is a professed whistle-blower — the Edward Snowden of banking — who has been hunted by Swiss investigators, jailed by Spaniards and claims to have been kidnapped by Israeli Mossad agents eager for a glimpse of the client data he stole while working for a major financial institution in Geneva.

“I am weak and alone,” Mr. Falciani said, as three round-the-clock bodyguards provided by the French government looked on with hard stares. The protection was needed, he insisted, because he faces constant risk as the sole key to decipher the encrypted data — five CD-ROMs containing a list of nearly 130,000 account holders that may be the biggest leak ever in the secretive world of Swiss banking.

But as he settled into a deserted bistro for a two-hour lunch, Mr. Falciani, a former computer technician who has been on the run since 2008, seemed oddly relaxed for a fugitive. And why not?

He is in high demand these days, having cast himself as a crusader against the murky world of Swiss banking and money laundering. Once dismissed by many European authorities, he and other whistle-blowers are now being courted as the region’s governments struggle to fill their coffers and to stem a populist uprising against tax evasion and corruption.