Solved All Members are Receiving Updates to One Category

We help look after a very busy board with thousands of members. Yesterday afternoon, the site started behaving as if every single member had subscribed to one category. A post was added to the category and every member was sent an email informing them of the update. 2 further updates were posted over the next couple of hours, and users were all emailed again. A total of nearly 20000 emails were sent out causing lots of complaints, confusion and our server has ended up on a few email blacklists. Has anyone else seen this, and is there any explanation for how this could have happened? We have disabled the category for now, but are concerned it could recur.

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Kunena version detailed: Kunena 4.0.10 | 2016-02-18 [ Villavicencio ]
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