Both Sky and BT successfully complained about c laims on the broadband section of the Virgin Media website, which said it offered u nlimited potential to "download and browse as much as you like with no caps and no hidden charges" .
The two firms, along with 20 members of the public, challenged Virgin Media over whether the "unlimited" claims in adverts were misleading and could be substantiated.
Sky also challenged whether the claim "no caps" in one advert misleadingly implied that there were no provider-imposed restrictions on a customer's ability to download data.
The ASA upheld the complaints, stating the adverts must not appear again in their current form.
The ruling said: "We told Virgin Media not to claim their services were 'unlimited' and with 'no caps' if they imposed restrictions that were more than moderate."
Virgin Media said the adverts, for their cable broadband services, were subject to a traffic management policy (TMP) - which could reduce a customer's download or upload speed for a short time.
Virgin Media provided a copy of a press release by comparison service uSwitch, which it said showed research supporting its belief that the TMP was moderate and its "unlimited" claim had been substantiated and was not misleading.
Virgin Media said it was common within the telecoms industry to refer to broadband and mobile services as "capped" or having "usage caps", "data download caps" or similar and that exceeding those caps meant consumers were charged or prevented from using that particular service.
The firm also confirmed its broadband services were not subject to any caps on the amount of data customers could download and it did not charge an additional fee once those thresholds were reached. Its customers could download as much as they liked without being subject to additional charges for use above a specified level, the company said.
Virgin Media said it thought the reference to "no caps" appeared in conjunction with its unlimited downloads claim with small print referring to the TMP. It believed that when the full claim was read in context, it was entirely clear as to what "no caps" referred.
But upholding the complaints, the ASA described Virgin Media's claims as "strong", and agreed the adverts had been misleading.