What are the most dangerous forms of social engineering?

One of the most dangerous forms of social engineering is the Internet activity called "phishing." The term comes from the analogy that attackers are fishing for information the way phone "phreaks" used to manipulate telephone numbers to gain free calls. Phishing attacks use email or malicious web sites to solicit personal, often financial, information. The attacker may send email seemingly from a reputable credit card company or financial institution that requests account information, often suggesting there is a problem. When a user responds with the requested information, the attacker uses it to gain access to the accounts.