The SANS Diary has an excellent entry on just how valuable social engineering is to attackers whether during penetration testing or as part of real world attacks. It explores the techniques used to marry offline social engineering lures with online attacks and the clever real world attack techniques that can end with malware installation on a computer system. Read the full diary [sans.org: Why bother breaking down the door if you can simply ask to be let in? Click here for the latest edition of the SANS diary.
Source: https://threatpost.com/social-engineering-real-world-computer-attacks-102709/72712/