Layer 7 devices used to prevent specific types of html tags are called:

A.
Firewalls

B.
Content filters

C.
Routers

D.
NIDS

Explanation:
A content filter is a is a type of software designed to restrict or control the content a reader is authorised
to access, particularly when used to limit material delivered over the Internet via the Web, e-mail, or
other means. Because the user and the OSI layer interact directly with the content filter, it operates at
Layer 7 of the OSI model.
Incorrect Answers:
A, C, D: These devices deal with controlling how devices in a network gain access to data and permission
to transmit it, as well as controlling error checking and packet synchronization. It, therefore, operates at
Layer 2 of the OSI model.

http://en.wikipedia.org/wiki/Content-control_software#Types_of_filtering
http://en.wikipedia.org/wiki/OSI_model