If you see a message on Facebook offering you a $25 iTunes Giftcard for completing a survey, ignore it - it is most probably a scam.

Security researchers at Sophos warned that while the people behind the scam were making money from every suvery completed, there was no chance that respondents would get the promised prize.

Graham Cluley of Sophos warned: "The scammers earn commission for every survey they trick people into completing - and your chances of ever receiving an iTunes Giftcard are close to zero."

However, should you click on the link you will arrive on a webpage which urges you to 'Share' the message with your Facebook friends before you can go any further.

This means the same message will be posted on your wall, where it will be visible to all of your friends. Should any of your friends fall for the scam, the message will be posted on their wall too, spreading the scam even further.

"Of course, if you have fallen for the scam, it's a good idea to remove all references to it from your Facebook page and warn your friends not to participate in it," Cluley advised.