I'd like to trace the viral pathways of a rumor. And it's a cracker of a rumor: that Meir Dagan, the Mossad Chief, was assassinated in Amman, Jordan, and his killing was hushed up. The story began circulating around the Middle East today at a scorching velocity.

And that's because aspects of it seemed plausible.

Dagan's portly face and penetrating eyes may be too well-known for him to take part in an actual spy operation (Israeli Channel 2 named him “Israeli Hero of the Year' for presumably ordering the hit on Hezballah's military commander Imad Mugniyah in Damascus). But Dagan does sometimes travel to Amman to exchange whispers with fellow spymasters. It is also true that Hezballah has sworn revenge for Mugniyah's killing, and the Mossad chief would make a fitting target.

Yesterday, the story started making the rounds on a few Arab internet sites. Then, according to one diplomat, it was picked up by DEBKAfile, a rightwing Israeli website, one of whose sensational –-and false-- reports about an impending terrorist attack in Manhattan actually prompted police to close down N.Y.'s bridges for several hours.

This time, DEBKAfile reported that: “on Oct. 12, Meir Dagan, the head of Israel's external intelligence service, the Mossad, was targeted by assassins while visiting Amman. Some describe a large bomb explosion alongside his convoy and add that Israeli and Jordanian guards with the convoy were injured. Others say Dagan himself was hurt or even killed in the attack. They claim Israel and Jordan are keeping the incident a secret.”

And who's a faithful reader of DEBKAfile? The Iranians. They picked up the news about Dagan's supposed death and spun it out into the blogosphere, where Arab media networks picked it up and gave the story traction. Camera crews raced out to Amman airport to see if there were Israeli aircraft flying in and out. Amman diplomats frantically rang their official contacts. Nothing. The rumor gained such credence that the Jordanian Interior Minister summoned diplomats to deny it.

In Israel, officials also nixed the report –-which, admittedly, they would even if it were true-- but as one source told TIME: “If the head of Mossad were killed by assassins, you couldn't keep it quiet. It would make a huge splash –-like throwing a boulder in a pond.”

In this age of cell-phones and instant Internet connectivity, it doesn't take long for stories to whizz around, and often, the speed at which they travel gives them an illusory substance, a specific weight and gravity, that really doesn't exist. But in this case, I can't help but wonder: what sparked the rumor of the Mossad chief's death? Was it pure mischief or something else? Stay tuned.

By Tim McGirk/Jerusalem