The BBC has closed a loophole on its iPlayer that allowed users to share programmes with others.
The iPlayer allows viewers to watch BBC TV programmes via the web but, because of stringent copyright rules and Digital Rights Management (DRM), viewers can keep the programmes on their hard-drive for only seven days after broadcast.
However, hackers managed to circumvent the anti-piracy controls using a simple plug-in for web browser Firefox and extend the time period to 30 days.
The BBC has announced that it has now fixed the problem, and that it didn't know how many programs had been downloaded using the hack.
"It's an ongoing, constant process and one which we will continue to monitor," said the BBC in a statement.
"Like other broadcasters, the security of rights-protected content online is an issue we take very seriously," it added.