A mysterious code reportedly appeared in some pirated streams of Saturday’s much-hyped fight between Floyd Mayweather Jr. and Conor McGregor, sparking suspicions that someone was trying to find out who was watching the illegal streams.

Saturday’s clash at the T-Mobile arena in Las Vegas was touted as potentially “the most pirated event in history,” and had already sparked legal action by Showtime Networks, which distributed the fight via Showtime Pay-Per-View.

Copyright and filesharing news site TorrentFreak said it had received an unsubstantiated report that “an unusual watermark” was embedded into streams originally broadcast by Sky Sports Box Office, which was licensed to show the fight in the U.K. Two other unnamed sources watching pirated streams also told TorrentFreak that the mysterious number and letter-based codes had briefly appeared on their screens too.

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“It’s certainly possible that the sequence of numbers would allow Sky to track the illicit stream back to a subscriber and/or a set-top box tied to a particular account,” wrote TorrentFreak. “Since that subscriber has then re-streamed that content back online illegally, the code would act as a homing beacon and could spell bad news for the individual involved.”

Sky Sports Box Office declined to comment on this story when contacted by Fox News.

Watermarks similar to the one in the stream are used in the broadcast industry. TorrentFreak, however, speculated that the code may have also been inserted by someone in the illegal streaming market who wanted to keep a tab on the stream. Illegal streams, TorrentFreak notes, can also be ‘stolen’.

There was huge global interest in the super-welterweight fight, which marked 40-year-old Mayweather’s return to the ring and the boxing debut of UFC Champion McGregor. After enduring an early barrage from his 29-year-old opponent, Mayweather wore McGregor down as the fight progressed. The 12-time world champion defeated the Irish MMA superstar by Technical Knockout when the referee ended the fight in the 10th round.

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Numbers on the subscribers paying to view the fight on legitimate streams have not yet been released.

Two years ago, Mayweather’s welterweight world championship unification fight with Manny Pacquiao, which was distributed by HBO and Showtime, set a new record of 4.6 million pay-per-view buys. However, Saturday’s clash was tipped to surpass this number.

Fox Business reported last week that pay-per-view purchases for Mayweather vs. McGregor could be in the neighborhood of 5 million buys.

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Eric Feinberg, a founding partner of deep web analysis company GIPEC, told Fox News that his company’s systems captured a number of pirated streams of Saturday's fight on Facebook Live and YouTube Live, some of which had over 25,000 paid views. “It’s an extremely big deal,” he said, noting the implications of pirated streams across a variety of sports. “It’s billions of dollars at risk … if you take one stream down, another one will come up.”

Last week, Facebook told Fox News that it devotes "significant resources" to addressing copyright issues for live content on the platform. "Video publishers and media companies can provide reference streams of live content that are checked against files in our Rights Manager tool," explained a Facebook spokesperson, in a statement emailed to Fox News. "If a match surfaces, Rights Manager immediately takes action on the rule set by the rights holder – for example, to block that stream."

The spokesperson added that rights holders can also report live videos at any time during a live broadcast. "We've been growing our global team that processes these reports across time zones and continue to invest in our copyright tools," he said. "This remains a work in progress and we continue to listen to feedback from our partners to help improve our offerings.”

Follow James Rogers on Twitter @jamesjrogers