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An embarrassing leak has enabled Shortland Street fans to see three alternative endings revealing the identity of the popular New Zealand soap's serial killer.

Fans of the show have been eagerly awaiting the December 14 season finale to find out the identity of the Ferndale Strangler.

But for a short time last week, anyone browsing the popular YouTube internet video was able to watch three possible endings.

The plot has kept viewers gripped this season as popular characters, including hospital administrator Claire Solomon (played by Emily Robins) and Jay Copeland (played by Jaime Passier-Armstrong) fell victim to the strangler.

The company that makes the show, South Pacific Pictures, moved quickly to have the clips removed from YouTube. They have been replaced by a message saying, "This video is no longer available due to a copyright claim by South Pacific Pictures".

South Pacific Pictures chief executive John Barnett said yesterday he was shocked at what had happened.

He learned of the YouTube postings on Friday, and they were removed soon after.

But he said the ending hadn't been ruined - viewers still didn't know for sure who the killer was because they didn't know which ending would be used.

"I'm worried that it's out there but there were three endings. The fortunate thing is that nobody is sure which of the three people it is."

He doesn't know how the endings got on to YouTube, but said he had a pretty good idea who was responsible.

"We know a whole lot of people who it can't be. We'll have a look [today] and check around. We know how many people have access to the actual ending so it's important that doesn't get leaked."

He wouldn't say whether the person responsible would lose their job.

And he doesn't know how many people saw the endings but is confident they won't be appearing anywhere else.

"It's annoying but it's not as annoying as if it was the actual final determinate ending."

The new Shortland Street season starts on January 14.