Comcast Official Blocked Ports

Port: 25 (TCP/UDP)

Port 25 is unsecured, and Botnet spammers can use it to send spam. If your computer has been compromised, our anti-spam system will prevent your email programs (e.g. Outlook Express) from sending email. You'll still receive email. This doesn't apply to webmail services such as Comcast webmail, Yahoo and Gmail. We recommendconfiguring your email program to use port 465 w/ SSL enabled.

Port: 68 (UDP)

UDP Port 68, which is used to obtain dynamic Internet Protocol (IP) address information from our dynamic host configuration protocol (DHCP) server, is vulnerable to malicious hacks.

Port: 135-139 (TCP/UDP)

NetBios services allow file sharing over networks. When improperly configured, ports 135-139 can expose critical system files or give full file system access (run, delete, copy) to any malicious intruder connected to the network.

Port: 445 (TCP)

Port 445 is vulnerable to attacks, exploits and malware such as the Sasser and Nimda worms.

Port: 520 (TCP/UDP)

Port 520 is vulnerable to malicious route updates, which provides several attack possibilities.

Port: 1080 (TCP)

Port 1080 is vulnerable to, among others, viruses, worms and DoS attacks.