Banned subliminal messages that could potentially manipulate users' subconscious have appeared in spam, according to PandaLabs.
Users opening the message see what appears to be a normal advertisement for online stocks. Yet the message also displays a rapid series of images, for 10 to 40 milliseconds, which include the word "buy", according to PandaLabs.
Controversy has surrounded subliminal messages since they were reportedly tested in advertising in the 1950s in the US. Nobody has ever shown that they work but subliminal images are banned worldwide in TV and cinema advertising.
Even though the spam recipient is not aware of the images, they can be influenced by them without realising it, according to Luis Corrons, director of PandaLabs. "This is the first time we have detected an Internet threat that uses subliminal techniques."
Subliminal techniques could become more sophisticated, he warned. "Think about the damage that this type of message could cause, especially to young users," he said, adding a suggestion that "appropriate security tools which include antispam and content filtering technologies will help prevent threats like this from reaching users' mailboxes."
Only a few examples of subliminal advertising have been tried. Campaigners for President Mitterand reportedly edited single-frame insertions of his portrait into French news broadcasts in 1988, while police in America tried to use the technique to catch a serial killer in 1978. Kansas TV station KAKE-TV transmitted a subliminal message for the murderer to turn himself in: his subsequent arrest in 2005 is not thought to be connected to the experiment.