The Advertising Standards Authority has ruled an ad for Onspeed that read: "Broadband Speeds for only £24.99 a Year" misleading.
Onspeed software compresses data, making certain parts of web use faster.
The ASA said that while the limitations of Onspeed were noted in a document on the website, it considered that the ad did not make clear that Onspeed would only increase the speed of web browsing and the sending and receiving of e-mails.
It said that consumers might infer from the ad that all aspects of their internet connection would benefit from an increase in speed.
The ASA said Onspeed needed to ensure that future advertising for the product made it clear that it would only speed up web browsing and the sending and receiving of e-mails.
www.asa.org.uk