McCann Erickson launched the campaign on behalf of Skcin to raise awareness of the growing threat of skin cancer.
Using print and outdoor ads, street leafleting, PR and digital seeding McCann Erickson and Skcin launched a fake company called ComputerTan, offering people the chance to get regular top-up tans from the comfort of their office desk using "revolutionary new technology".
The fake ComputerTan.com site allows people to switch on what they expect to be a free tanning session but once the screen has converted to an array of UV bulbs users are confronted with shocking images and facts about skin cancer as well as a link to Skcin's website for more information.
The hoax launched on February 3 and will run until February 9 when Skcin will reveal how many people were enticed into visiting the site with the offer of a free trial of the tanning service via their computer screen.
The charity hoped that the media would play along with the hoax until the later date, but The Sun carried a story today explaining who was behind it.
McCann Erickson created an infomercial film fronted by fictional ComputerTan spokeswoman Hannah Yasmin, who tells her audience how they can look "Tan-tastic" and offers a free trial of the service via the website.
The 20 second ad is also running on CBS Outdoor's digital network on the London Underground using 75 cross track screens at 11 stations over two weeks.
The strategy, developed by McCann Erickson with viral marketing agency Rubber Republic, included online seeding of the film on hundreds of sites and persuading influential bloggers to join in the hoax.
McCann Erickson claims to be on track to reach 100,000 hits by the end of the first week and aims to reach 1m over the course of the two week campaign. So far users are spending well over a minute on the site on average.
CBS Outdoor's cross-track projection sites are reaching 1.7m commuters a day in London and the digital campaign has generated in excess of 8,000 references on Google in the first day of activity.
Simon Hill, new business director at McCann Erickson, said: "This campaign was designed to engage those most at risk of developing skin disease and those most difficult to talk to via conventional advertising.
"The fact that so many people fell for the ComputerTan hoax demonstrates the frightening truth that getting a tan -- regardless of the risk -- is still appealing for many people."
Richard Clifford, co-founder of Skcin, said that the campaign is a humorous way to raise awareness of a very serious issue.
He said: "More people die of skin cancer in the UK every year than in Australia. It is the most common form of cancer in young adults (15 - 34) and is largely preventable.
"The lack of regulation concerning the use of sunbeds is an extremely serious issue that has a comparatively low profile, and this campaign highlights the fact that it is high time for a change in the law."