CANNES, France — Viral advertising is spreading as a popular, efficient marketing tool, as consumers increasingly pick and choose what ads they watch and when.

Viral is today's electronic equivalent of old-fashioned word of mouth. It's a marketing strategy that involves creating an online message that's novel or entertaining enough to prompt consumers to pass it on to others — spreading the message across the Web like a virus at no cost to the advertiser.

Marketers have caught the bug and are increasingly weaving viral components into their marketing plans. Not only is the approach relatively inexpensive, but also it can sometimes be more believable than standard ads.

“People have grown increasingly skeptical of packaged, canned, Madison Avenue-speak,” says Russ Klein, Burger King's chief marketing officer.

The company has reversed a long sales decline thanks in part to its increased use of non-traditional marketing, especially viral. It has proved particularly useful in reaching the fast-food chain's core market of young men.

The key to effective viral: Create and execute an idea that's intriguing enough to get consumers to interact. Burger King has used wacky ideas by agency Crispin Porter + Bogusky to promote its chicken sandwiches and salads online.

“Interruption or disruption as the fundamental premise of marketing” no longer works, says Jeff Hicks, chief executive and partner at Crispin Porter + Bogusky. “You have to create content that is interesting, useful or entertaining enough to invite (the consumer). Viral is the ultimate invitation.”

Hicks' agency on Wednesday won the Grand Prix (best overall), as well as four Cannes Lions, in the online ad category at this week's International Advertising Festival here. The annual competition honors the world's best advertising in eight categories.

Brewer Anheuser-Busch has hired Gregg and Evan Spiridellis to create Web entertainment this summer for Budweiser. They are the brothers who created This Land, an animated spoof of the presidential election that spread across the Web last fall eventually to be seen by an estimated 80 million viewers.

“All viral means … is that you've created a message that people want to share. It's proof that your message is resonating,” says Gregg Spiridellis, who co-founded animation and design studio JibJab with his brother. “If people want to pass it along, that's what brand marketing is all about.”

Though specific viral spending is difficult to measure, overall spending on Web advertising continues to rise. Last year, marketers spent $7.4 billion, a 21% increase over 2003, on Internet ads, according to TNS Media Intelligence.

While the Web can be effective, it also can bite back. Consumers can spread gripes about a brand just as easily.

“Advertisers are not nearly in control of their brand message as they think they are,” says Klein. “When you are out there living in that world, they are not always going to say nice things about you. You can't get too uptight about how you manage the conversation.”

Viral also takes off best with a boost, cautions Hicks: “Where you really get the ‘one plus one equals three' is to include viral into the mix of media. Involving traditional media is an important step.” Advertisers trying to get consumers to “talk” among themselves:

The brand recognized for safe, conservative vehicles took a daring — for Volvo — approach to marketing by presenting on the Web a contrived story about a small town in Sweden where 32 folks bought new S40s in a single day.

Included was a “documentary” about the event, supposedly by faux film director Carlos Soto (who even had his own faux website).

The effort helped launch the entry-level luxury S40, which became a top-seller for Volvo last year.

“The whole idea was quite provocative and young,” says Tim Ellis, global advertising director.

“The unexpectedness of this very family-oriented, squeaky-clean brand doing something like this was interesting. People didn't really want to believe Volvo would do something like that.”

The goal was to make the release of Microsoft's xBox video game Halo 2 as big an event as the opening of a blockbuster movie.

To build such buzz, Chris DiCesare, director of marketing for Microsoft Game Studios, created a complex marketing scheme that began online with an apparent War of the Worlds-style invasion. A beekeeper's website, ilovebees.com, appeared to have been overtaken by the evil force — the Covenant.

The campaign then involved calling random pay phones, messaging and calling consumers' cellphones and blogs and live chats online. The game tallied first-day sales of $125 million last November.

“Since I couldn't go with the other regular marketing forms, I figured I would take a calculated risk with viral,” DiCesare says. “It was a small portion of my overall marketing budget but had the potential to show great return on investment, if it worked.”

Not since the movie Forrest Gump has shrimp had the potential to create such a buzz. The fast-seafood chain has launched shrimpbuddy.com, a website that features a two-minute, feel-good film about a road trip by a guy and his buddy, who is a shrimp.

The guy narrates a series of flashback images showing the two pals enjoying laughs, meals and traveling together. In the end, the guy eats his shrimp buddy at a Long John Silver's restaurant — to promote the chain's Popcorn Shrimp.

“Our new Popcorn Shrimp is a product that is going to appeal to a younger, hipper, on-the-go consumer,” says Don Gates, director of marketing for Long John Silver's.

“They're young; they're Web savvy; they have a great sense of humor.

“They're the kind of customers who will enjoy Road Trip with ShrimpBuddy. Heck, they're the kind of customers who'd enjoy going on a road trip with a shrimp buddy.”