Why does our facebook group's wall keep getting cleared? Hacked?

[Blacob]

I am part of a facebook group that is mostly political(where we have many who oppose us.) We had our group for many months when one morning we woke up to find our wall completely cleared. Then it got cleared every day from then on. We started a different group and that new one gets cleared every time a conversation actually starts. Clearly somebody is deleting our posts. When it happens all of the posts are cleared at the same time.
How does this happen? How can we stop it?

[James]

Whoever is the owner of the group needs to change their Facebook password because it's most likely a hacker.