Not too long ago I posted about MSN's new filters against programs with extensions commonly used to exploit Windows machines (like .pif, .scr, .com, etc).
It turns out that there is a really bad side-effect of all this new protection in a recent build of MSN. If you type a forbidden extension like ".pif" in a group conversation in MSN, it boots everyone out of the group conversation and closes the group conversation. Too funny.
You can read more on Messenger Blog. One of the comments gives the impression that this behavior is intentional, not a bug. In a way, I really hope not, but in a way, I really do; the more really strange things the other IMs do, the better BitWise looks. :)