Be Broadband has been found to be in breach of the Advertising Standards Authority's (ASA) code of conduct.
A member of the public who saw an advert on a social-networking website but found it to be for a product that had been discontinued three weeks beforehand.
The product, a broadband package that offered up-to-24Mbps connection for £14 per month with a capped usage, was replaced at the end of August 2007. However, the complainant saw the advert on 22 September.
Be Broadband said in its defence that the media-buying agency it had used was at fault and that it had been told that the adverts were no longer running.
But the ASA found that the advertising had been misleading and upheld the complaint.
"Because the product had been withdrawn at the end of August, we considered that the ad was misleading. We considered that it was Be's responsibility to ensure that product changes were communicated promptly to online media-buying agencies," the ASA said in its ruling.
The ASA added that it had told Be Broadband to "ensure that their online advertising accurately reflected their broadband packages in future."
Be Broadband, which is now owned by mobile operator O2, has an unbundled telephone network which it says reaches around 50 per cent of the UK's population, allowing it to offer services with speeds up to 24Mbps, rather than the 8Mbps ISPs using BT's network are limited to.
www.asa.org.uk www.bethere.co.uk