Some people have been going around messaging people in any Left 4 Dead related groups from Australia asking them to verify their account details or something.

This is the message I got "
:: Due to recent hack attempts we are monitoring steam accounts VERY closely. We have noticed 2 different IP address logged into your account recently. In order to verify that YOU are the correct owner we require you to log in (http://xxxxxxxxxxxxxxxxx.xx). Once you log in your ip will verify who you are and be set to your steam account."

Just incase you're new to Steam or love to fall for scams this is just a warning to you guys. Don't fall for that kind of crap.