Here are some popular sites for testing your PC/Internet/router network security:
The ever popular, ShieldsUp!
http://grc.com
NOTE: If you use ShieldsUp!, see https://www.routertech.org/kb.php?mode=article&k=20
Port scans
http://www.dslreports.com/scan
Firewall test etc
http://www.auditmypc.com/freescan/prefcan.asp
Sygate scans (several inc. Stealth, Trojan, TCP etc)
http://scan.sygate.com