If you're running OS X in a networked environment, then you have an auto-configured IPv6 connection to your network.
Unfortunately, IPv6 provides an opening for attackers to compromise your network. If you don't work for a large company that requires it, you can and should shut it off. Here's how to do it.
In OS X, open System Preferences, then Network.
Select the connection you’d like to modify (you’ll need to do each one in each location), and click Advanced.
Next to Configure IPv6, select Off from the drop-down menu.
After turning off IPv6, click OK.
Then close out of System Preferences.
Viola, you’ve mothballed IPv6 until you really need it.
If you're a Windows user, check out how to disable IPv6 in Windows 7.