Ya I think you just need to secure your wifi. They probably set it up "unsecured" because it is easier for the installer than to try to walk someone through all that.
Depending on the type of router and setup you have, you may also we able to specifically "assign" ip's to specific computers. This along with the password protected wifi is probably all if not more than you need.
But if you have friends coming over that need to use your wifi, assigning ip's may not be for you, as its not as easy as just saying "this is my wifi pw".
And what rwbradley said as well. :)