The other is to block the electronic path to objectionable material with filtering software.

ECONOMIST: China and the Internet

But because filtering programs use keywords to block material, they can inadvertently restrict content you want your children to access.

CNN: Tools: Protecting your kids online

"There's no guarantee that they are going to be able to get the offensive material out of the system quickly, " said Geoff Haggart, European head of filtering firm WebSense.

BBC: The problems of finding filth