Game of Thrones is the most-pirated TV show in the world, according to a four-week snapshot of online piracy shown to the Guardian.

The hit HBO show, returning for its fourth season on Monday, tops a list that features some of the most sought-after shows on television, including The Walking Dead, Breaking Bad and Mad Men.

The snapshot of global illegal downloading, carried out by anti-piracy and security firm Irdeto, found that Game of Thrones episodes were downloaded almost 1.6m times.

The fantasy show accounted for a quarter of the 7.5m illegal downloads of the 28 shows Irdeto tracked between 13 January and 9 February.

"Programmes start to be pirated literally minutes after the first airing of a show," says Eric Antze, product manager at Irdeto.

"Within an hour we see pretty significant propagation of that content across the internet, and piracy is on the increase."

Such data explains why HBO has allowed Game of Thrones to air at 2am on Monday on Sky Atlantic in the UK, the same time it is broadcast globally. Twenty years ago British viewers had to wait months for a hit US show such as Friends to reach British screens.

However, the TV industry does not see itself as following in the footsteps of music , which has been ravaged by illegal downloads. Jeff Bewkes, the chief executive of HBO's parent, Time Warner, has said Game of Thrones piracy has been "better than an Emmy" as a publicity machine which helped drive TV subscriptions."It is not as big of an issue as music in part because there is a plentiful supply of legal and free content out there," says John Enser, a partner at media law firm Olswang. "From the iPlayer, to 4oD and Sky's on-the-go services there are plenty of options, a lot of TV is free, and the UK is ahead of many countries including the US in offering 'TV Everywhere'".

Giles Willits, the financial chief of Entertainment One, which distributes shows including Walking Dead and new teen film Divergent, says that the digital age may have enabled piracy but it has also provided rights holders with huge opportunities.

"We see the move to digital as an opportunity to be able to monitor activity and there are also successful models for good paying citizens, like Netflix and Lovefilm," he says. "The majority of people want to be legitimate, they don't want to be seen as thieves or pirates. It comes down to a balance of piracy versus not being able to live in a world of $100m TV shows like Game of Thrones".