Rival internet service provider BT complained about three press ads, two TV ads and a radio ad, which appeared in October and November last year.
The ads claimed "Ofcom has proven our fibre optic broadband is around twice as fast as BT" and similar assertions, which BT said could be misleading.
The ASA upheld BT's complaint that the ads failed to prominently state which services were being compared.
BT said three members of the public challenged whether the claim, "fibre optic broadband from Virgin Media. The fastest in the UK", in the Speedy Gonzales TV ad could be substantiated since other providers offered a faster download speed.
ASA ruled Virgin's "absolute claim was misleading" because it was based on Ofcom findings that covered 90% of the UK market and because there were instances of niche providers and other ISPs providing trial products with speeds faster than Virgin's.
It also upheld BT's complaint for the radio ad, which claimed Virgin Media was twice as fast for shopping and tweeting, because download speeds are of limited importance for web browsing.
BT also challenged the radio ad's claim that Virgin Media was up to twice as fast for gaming, because the ad suggested internet connection speed was the only factor in achieving optimum game performance.
The ASA considered internet speed was a factor but other performance metrics, such as latency and packet loss, affected overall performance, therefore concluding the claim was also misleading.
Several of BT's complaints, including an allegation that the ads did not make a like-for like product comparison, were not upheld.
The ASA also declined to uphold complaints from members of the public that accused Virgin Media's maximum download speed of being lower than BT's.
The ASA adjudicated that the ads must not appear again in their current format.
Last month Virgin Media was banned from running a campaign that denigrated the broadband service offered by rivals, via a website Stopthebroadbandcon.com.