An open source advocate group is threatening the BBC with an European antitrust challenge to the digital rights management (DRM) technologies used in its on-demand iPlayer service.

The Open Source Consortium (OSC) has written to watchdog Ofcom, the Office of Fair Trading (OFT) and the BBC Trust, asking for a re-examination of the effects of the BBC's iPlayer service being tied into Microsoft Windows Media Player for at least two years and, by extension, new versions of Windows.

OSC chief executive, Iain Roberts said: "This action from the BBC effectively promotes one operating system vendor at the expense of others. It is very disturbing that the BBC should be using licence payers' money to affect the operating system market in this way. Imagine if the BBC were to launch new digital channels, but only make them available on a certain make of television – there would be uproar."

The OSC, who represents open source user advocates and vendors, compared the decision taken by the BBC Trust at the end of April to use a Windows-only broadband on-demand player to the ongoing action taken again Microsoft by the European Commission (EC) over its bundling of Windows Media Player with Windows.

The BBC has said in a statement it was necessary to use the Windows platform to ensure content could not be unlawfully distributed or viewed after 30 days. It also said it would look at making the iPlayer available for Mac users in future.

In other news today research from online market researcher Hitwise, YouTube is set replace the BBC as most visited general entertainment site for UK web surfers, if current trends continue.

Although the BBC currently leads the pack, the gap between the two is narrowing. The BBC site has been ranked as the number one entertainment website over the past two years and YouTube has held second position since October 2006. The BBC site currently ranks 14th among all categories of websites with 0.82% of UK internet visits compared to YouTube's ranking of 25th with 0.81% of visits.

The BBC currently allows a number of programme clips to be shown on YouTube. Earlier this week YouTube launched local sites including those covering UK and Ireland. The Hitwise report also shows that the entertainment category has overtaken the retail category in share of UK visits for the first time.

Additonal reporting by Nick Spence, Macworld.co.uk