said by a333 :

Uh-huh... sharing your connection is LEGAL,

Network and usage restrictions
....make available to anyone outside the Premises the ability to use the Service (for example, though wi-fi or other methods of networking), in whole or in part, directly or indirectly.

connect the Comcast Equipment to any computer outside of your Premises;

What obligations do I have under this Policy?
...you are also responsible for any use or misuse of the Service that violates this Policy, even if it was committed by a friend, family member, or guest with access to your Service account. Therefore, you must take steps to ensure that others do not use your account to gain unauthorized access to the Service by, for example, strictly maintaining the confidentiality of your Service login and password. In all cases, you are solely responsible for the security of any device you choose to connect to the Service, including any data stored or shared on that device.

It is also your responsibility to secure the Customer Equipment and any other Premises equipment or programs not provided by Comcast that connect to the Service from external threats such as viruses, spam, bot nets, and other methods of intrusion.