The service, which lets viewers watch or download BBC programmes from the internet, was created with digital rights management software that deletes shows from the website after one week and deletes downloaded files from the user's computer after 30 days.
However, hackers found a flaw in the DRM software for the iPlayer, allowing them to download television shows onto their computer without any copyright protection.
The BBC said it has now managed to close the loophole and prevent programmes from being accessed without anti-piracy protection, but that it will continue to monitor the situation.
A BBC spokeswoman said: "We've released a fix to prevent unrestricted downloading of streamed TV programmes on BBC iPlayer.
"Like other broadcasters, the security of rights-protected content online is an issue we take very seriously. It's an ongoing, constant process and one which we will continue to monitor."
The iPlayer service has been gaining rave reviews since it launched last year. The BBC claims that 17m programmes have been downloaded or streamed on demand via iPlayer since launch, which is up to 500,000 a day.
In January, more than 2.2m people watched a programme on the iPlayer, and about 11m programmes were streamed or downloaded..jpg)
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