Internet telephony service Skype has confirmed that a bug in its software has been sending copies of instant messages to unintended recipients.
After complaints from users that private messages sent using Skype's instant message service had been re-sent to other contacts, the company said this was happening in "rare circumstances", according to the BBC.
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Skype claims messages are forwarded to a third contact only when the Skype client crashes during a conversation. When that happens, the last IM entered or sent prior to the crash is sent to that unintended third contact, according to US reports.
Skype said it is working on the problem and will issue another software update in the next few days. Skype said it would prompt users to download and apply the update to prevent the problem spreading.
However users have been hit by the bug since June, when it is believed to have been introduced through a previous software update.
According to Skype the bug is confined to Skype 5.9 and 5.10 for Windows, 5.8 for Mac, 4.0 for Linux, 4.0 for iOS, 2.8 for Android, and 1.2 for Windows Phone.
In May 2011 a faulty software update was responsible for locking Skype users out of the internet telephony service. Some users were unable to login to the service for several days, but Skype said the number was small.
Skype claims to have around 30 million concurrent users at peak times of its service that enables voice and video calls to other users over the internet.
Skype was acquired by Microsoft in 2011 for $8.5bn.