NO sooner had Alex Rospos arrived from Los Angeles for a Memorial Day weekend on the Jersey Shore than he witnessed, and fell victim to, his first prolonged session playing what has become the nation’s biggest viral drinking game, otherwise known as “icing.”

It began six hours after he arrived — “I iced a friend at lunch,” he said — but really took off at a barbecue around the family pool in Belmar the next day. “There have been over 20 icings so far,” Mr. Rospos, a 25-year-old aerospace engineer said, a beer cozy carrying a warm bottle of Smirnoff Ice clipped to the back of his belt with a carabiner. “You have to watch yourself.”

The premise of the game is simple: hand a friend a sugary Smirnoff Ice malt beverage and he (most participants have been men) has to drink it on one knee, all at once — unless he is carrying a bottle himself, in which case the attacker must drink both bottles of what Mr. Rospos described as a “pretty terrible” drink.

Amid suspicion that the trend is an elaborate viral marketing campaign by Smirnoff, which the company has denied, new icing photos are posted daily on various blogs, Twitter and Facebook — including scenes from graduations and weddings — and sent directly to a Web site, BrosIcingBros.com. The speed with which Mr. Rospos and a group of his friends from high school adopted the game mirrors the rapid spread of Bros Icing Bros from the Web to backyards, living rooms and cubicles around the country, exploding from obscurity in May into a bizarre pastime of college students, young professionals and minor celebrities that counts among its targets the rapper Coolio, the actor Dustin Diamond and members of the rock band The National. A campaign online aims to ice Ashton Kutcher, who often serves as a kind of Kevin Bacon of Web memes, linking disparate areas of the Internet in fewer than six degrees.