Personal Firewall is a popular and common installation choice on personal computers nowadays. It is expected to provide higher Internet security by employing Internet access controls. In this paper, we discuss the insecurity of most personal firewalls on Microsoft Windows platform and the methodologies to bypass them. We show that personal firewalls can be bypassed using various methods at different layers in Windows Network Architecture. We reckon that in order to better secure personal computers, more effective methods have to be implemented to enforce the security strength of personal firewalls. In addition, personal firewalls should be used in conjunction with good antivirus programs to provide in-depth security defenses.