Windows 7 - Unknown new network connections

In Windows Explorer, at the bottom of the left column, I just noticed today new computers in my network with some computers I don't know and didn't add. One of them has a password on it, and one of them I can just look at files on some guy's PC, and I'm worried that they could do the same to me. How did they get there, how do I get rid of them, and how can I prevent it from happening again?

Sounds like someone is borrowing your unsecured wireless connection. If you are using a wireless router then you need to enable the security, WPA-2 is best, and also create a wireless access password which is standard procedure when ever you set up a wireless network. You will need to access your routers set up page for this.

Also when you set up your wireless connection in Windows 7 "assuming you are using wireless" you will have options to enable WPA-2 which you need to do, and also type in the wireless password. It's easy to figure out.

If you keep having problems you can also set your SSID "wireless network name" to not broadcast.