YouTube has become embroiled in the alleged equivalent of a vote-rigging scandal after a banal music clip became the most popular video in the site's history, in what many believe were suspicious circumstances.

The clip, which features a song by the Brazilian dance act Cansei De Ser Sexy (CSS), was posted on the video-sharing site last year by an Italian blogger after he entered a competition run by an Italian music channel.

By early February, the three-minute clip, which features the track Music Is My Hot Hot Sex, had had 40 million views, but over the course of a single month it attracted 40 million more - taking it past the clip that was until then the most popular - Evolution of Dance - which has been seen 79 million times.

YouTube appears to have removed the clip from its 'most popular' list in early March pending an investigation, but the video was also subsequently taken down by its creator, Clarus Bartel, who started receiving angry messages from fellow users accusing him of cheating the site's rankings.

Bloggers have suggested that the by all accounts undistinguished clip - which shows the band performing the song in front of a series of screens that gradually change colour - could have become so popular in the traditional fashion: by being widely recommended on both websites and by e-mail.

According to one Los Angeles-based writer, Andy Baio, one of the signs that the clip's meteoric rise was suspicious was its 'views to ratings' ratio. Most highly popular videos on YouTube were given a rating by a viewer about every 500 times they were watched, Mr Vaio calculated, but in the case of Mr Bartel's clip, only one in every 21,000 views resulted in a rating.

This lack of feedback suggested it was "extremely unlikely" that the video, which YouTube's site at one point suggested had been seen more than 114 million times, was attracting traffic from "legitimate external sources," Mr Vaio wrote on his blog Waxy.org.

Contacted by Times Online yesterday, Mr Bartel said he had been completely overwhelmed by the attention his film had received, and that he had no explanation for why it had become so popular. He suggested it may have been because he 'tagged' the clip with the words 'hot' and 'sex' - both from the name of the CSS track - which could be popular search terms on YouTube.

Mr Bartel also said the video may have brought traffic from users looking for the new advertisement for Apple's iPod touch, the combined music player and internet browser, which had featured the same music.

At about the same time that the clip was becoming popular, Apple revealed it had recruited an 18-year-old university student from Warwick to help make an ad for the iPod Touch. Mr Bartel said his video - which was also tagged with the words 'iPod' and 'touch' - may have picked up search queries for Apple's ad.

Asked whether the viewing figures for his video may have been artificially inflated, Mr Bartel, who is Italian, said: "These gimmicks do not belong to me. I've got nothing to do with it. The accusations geared towards me have saddened me greatly."

YouTube, which has investigated the matter, would not say whether its rankings system had been cheated. In a statement, the site, which is owned by Google, said: "We don't condone efforts to affect the integrity of our video."

Tony Kiewel, head of A&R at Sub Pop, CSS's record label, which authorised film-makers to use the band's music for the competition, said: "Everything seems to point to the system having been gamed - but it's just not clear who would be benefiting."

A financial motive can be ruled out - YouTube does not allow its users to share in the site's advertising revenues unless they are official YouTube partners, and Mr Bartel was not such a partner.

"It's not outside the realm of possibility that there could be a legitimate explanation, especially if it's been tagged with words like 'hot' and 'sex', but it certainly is a mystery," Mr Kiewel said. "We'd be curious to find the answer."

Evolution of Dance, a 6-minute clip which shows the stand-up comedian Judson Laipply demonstrating several decades' worth of dance moves, has been the most viewed video on YouTube for about 18 months.

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