Internet Blocking Software
Internet blocking software (a.k.a. Internet content filter) is a software that uses Internet blocking technologies to achieve Internet control such as to block inappropriate internet activities.

Two Internet Blocking Technologies
Internet blocking software (Internet content filter) can use two different Internet blocking technologies to perform internet control: Passive and Active.

Passive Internet Blocking Technology (a.k.a. Pass By)
This an Internet blocking technology that will not require to change network infrastructure/configuration and client PC.This internet blocking technology does not pose an additional delay and bottleneck for the network.

Active Internet Blocking Technology (a.k.a. Pass Thru)
This is an Internet blocking technology that may require an additional layer on the network configuration that behaves like a gateway.This internet blocking technology will pose an additional delay and bottleneck for the network.

Note that 2Watch Internet Filter (Web Filter) uses Passive Internet Blocking technology