How Hackers get you through Social engineering?

Social engineering is the act of manipulating people into performing actions or divulging confidential information. While similar to a confidence trick or simple fraud, the term typically applies to trickery or deception for the purpose of information gathering, fraud, or computer system access; in most cases the attacker never comes face-to-face with the victim.

Social engineering techniques and terms

All social engineering techniques are based on specific attributes of human decision-making known as cognitive biases. These biases, sometimes called "bugs in the human hardware," are exploited in various combinations to create attack techniques, some of which are listed here:

Pretexting

Pretexting is the act of creating and using an invented scenario (the pretext) to persuade a targeted victim to release information or perform an action and is typically done over the telephone. It is more than a simple lie as it most often involves some prior research or set up and the use of pieces of known information (e.g. for impersonation: date of birth, Social Security Number, last bill amount) to establish legitimacy in the mind of the target. 
This technique is often used to trick a business into disclosing customer information, and is used by private investigators to obtain telephone records, utility records, banking records and other information directly from junior company service representatives. The information can then be used to establish even greater legitimacy under tougher questioning with a manager (e.g., to make account changes, get specific balances, etc).
As most U.S. companies still authenticate a client by asking only for a Social Security Number, date of birth, or mother's maiden name, the method is effective in many situations and will likely continue to be a security problem in the future.
Pretexting can also be used to impersonate co-workers, police, bank, tax authorities, or insurance investigators — or any other individual who could have perceived authority or right-to-know in the mind of the targeted victim. The pretexter must simply prepare answers to questions that might be asked by the victim. In some cases all that is needed is a voice that sounds authoritative, an earnest tone, and an ability to think on one's feet.

Phishing

Phishing is a technique of fraudulently obtaining private information. Typically, the phisher sends an e-mail that appears to come from a legitimate business—a bank, or credit card company—requesting "verification" of information and warning of some dire consequence if it is not provided. The e-mail usually contains a link to a fraudulent web page that seems legitimate—with company logos and content—and has a form requesting everything from a home address to an ATM card's PIN.
For example, 2003 saw the proliferation of a phishing scam in which users received e-mails supposedly from eBay claiming that the user’s account was about to be suspended unless a link provided was clicked to update a credit card (information that the genuine eBay already had). Because it is relatively simple to make a Web site resemble a legitimate organization's site by mimicking the HTML code, the scam counted on people being tricked into thinking they were being contacted by eBay and subsequently, were going to eBay’s site to update their account information. By spamming large groups of people, the “phisher” counted on the e-mail being read by a percentage of people who already had listed credit card numbers with eBay legitimately, who might respond.

IVR or phone phishing

This technique uses a rogue Interactive voice response (IVR) system to recreate a legitimate sounding copy of a bank or other institution's IVR system. The victim is prompted (typically via a phishing e-mail) to call in to the "bank" via a (ideally toll free) number provided in order to "verify" information. A typical system will reject log-ins continually, ensuring the victim enters PINs or passwords multiple times, often disclosing several different passwords. More advanced systems transfer the victim to the attacker posing as a customer service agent for further questioning.
One could even record the typical commands ("Press one to change your password, press two to speak to customer service" ...) and play back the direction manually in real time, giving the appearance of being an IVR without the expense.
The technical name for phone phishing, is vishing.

Baiting

Baiting is like the real-world Trojan Horse that uses physical media and relies on the curiosity or greed of the victim.
In this attack, the attacker leaves a malware infected floppy disk, CD ROM, or USB flash drive in a location sure to be found (bathroom, elevator, sidewalk, parking lot), gives it a legitimate looking and curiosity-piquing label, and simply waits for the victim to use the device.
For example, an attacker might create a disk featuring a corporate logo, readily available off the target's web site, and write "Executive Salary Summary Q2 2009" on the front. The attacker would then leave the disk on the floor of an elevator or somewhere in the lobby of the targeted company. An unknowing employee might find it and subsequently insert the disk into a computer to satisfy their curiosity, or a good samaritan might find it and turn it in to the company.
In either case as a consequence of merely inserting the disk into a computer to see the contents, the user would unknowingly install malware on it, likely giving an attacker unfettered access to the victim's PC and perhaps, the targeted company's internal computer network.
Unless computer controls block the infection, PCs set to "auto-run" inserted media may be compromised as soon as a rogue disk is inserted.

Quid pro quo

Quid pro quo means something for something:

• An attacker calls random numbers at a company claiming to be calling back from technical support. Eventually they will hit someone with a legitimate problem, grateful that someone is calling back to help them. The attacker will "help" solve the problem and in the process have the user type commands that give the attacker access or launch malware.

• In a 2003 information security survey, 90% of office workers gave researchers what they claimed was their password in answer to a survey question in exchange for a cheap pen. Similar surveys in later years obtained similar results using chocolates and other cheap lures, although they made no attempt to validate the passwords.

Other types

Common confidence tricksters or fraudsters also could be considered "social engineers" in the wider sense, in that they deliberately deceive and manipulate people, exploiting human weaknesses to obtain personal benefit. They may, for example, use social engineering techniques as part of an IT fraud.
The latest type of social engineering techniques include spoofing or hacking IDs of people having popular e-mail IDs such as Yahoo!, GMail, Hotmail, etc. Among the many motivations for deception are:

• Phishing credit-card account numbers and their passwords.
• Hacking private e-mails and chat histories, and manipulating them by using common editing techniques before using them to extort money and creating distrust among individuals.
• Hacking websites of companies or organizations and destroying their reputation.