An Extranet Is

An extranet is

A) a web monitoring tool that provides an "extra net" of protection against malware and viruses.
B) a restricted website available to employees and to outside parties by invitation only.
C) another name for a social network such as LinkedIn.
D) another name for the hidden internet, which standard search engines do not reach.
E) a network tool that allows employers to "ping" website users and monitor their activity.