Which of the following security threats is BEST mitigated through proper user training?

Which of the following security threats is BEST mitigated through proper user training?

A.
A Worm

B.
Rootkits

C.
Social Engineering

D.
Browser Adware

Explanation:

Reference:
http://www.veracode.com/blog/2013/03/hacking-the-mind-how-why-social-engineeringworks/