MSN and Windows Live Messenger block any urls containing '.scr', probably to stop a common virus spreading along the servers. This method has probably helped many, however the censoring of messages is seen as bad.

Why? Well because the feature is no way coded correctly. Basically the security feature does what it says on the tin, blocks urls containing .scr, and nothing else. Your contact will not receive your message, and you will not be alerted that your message has been blocked. Something which can be confusing and frustrating.

This is just one example, many other things are blocked within your messages. Good luck sending a message with staff.php, and I'll think twice before typing .pif into a conversation. Typing .pif is really annoying, I just wish Messenger would block the extension in a file transfer, but it's useless blocking sending 'pif' in a message. I know it is to stop urls with .pif in them, but urls can be masked, or redirect to a virus. This security feature is just an annoyance.

Typing .pif into multiple conversations was just ridiculous. It used to kick everyone out, it would totally end the conversation, and some prankster would do it just to annoy people. A fix is now just kicking you out, which is not a fix, just a temporary solution which needs to be tackled.

If any Windows Live Messenger developer reads this, next time a message is blocked for security reasons, make sure the user knows, and why. It will stop a lot of confusion, and may stop you getting your company into trouble. Many people have moaned in blogs about how Messenger blocks out certain words and extensions, and the majority are not for good reasons. Think more user-friendly, it is something very important nowadays.