The advertising watchdog has criticised Sony for running a competition to buy a limited edition PlayStation 4, after a number of winners found a way to scam the online entry system.

Sony ran an online competition giving the first 100 entrants a day answering a clue the chance to buy a limited edition PS4.

If a consumer got a clue correct they were linked to a page with a submission form to buy the console, which was hosted online by the high street retailer Game.

However, the web address for the submission page was not unique to each person who entered the competition, meaning it could be shared and people who didn’t even attempt to answer the clue could submit to win a PS4.

Sony said that during the competition it put measures in place once it discovered that people were using computer programs to gain early access to the web address.

Although the competition was meant to only allow one PS4 for each customer, five consumers had been able to purchase two consoles a piece during the promotion.

The Advertising Standards Authority received six complaints challenging whether the competition had been administered fairly.

“Although processes had been put in place to try to prevent consumers from purchasing more than one console, at least five consumers had been able to do so, against the promotion’s terms and conditions,” the ASA said in its ruling. “A link to the opportunity to purchase the console could be shared, which meant that neither Sony nor Game could tell whether consumers had accessed the link after having solved the clue, or having been sent the link.”

The ASA said that meant entrants who played the game fairly were “disadvantaged and therefore unnecessarily disappointed”.

The ad watchdog said the promotion had not been administered fairly and was in breach of the sales promotions and administration rules of the advertising code.