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Spear phishing is targeted. The attackers did their research, usually through social engineering. They might already know your name or your hometown, your bank, or your place of employment—information easily accessed via social media profiles and postings. That bit of personalized information adds a lot of credibility to the email.

Spear-phishing emails work because they’re believable.

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Spear-phishing attacks are not trivial or conducted by random hackers. They are targeted at a specific person, often times by a specific group. Many publicly documented advanced persistent threat (APT) attack groups, including Operation Aurora and the recently publicized FIN4 group, used spear-phishing attacks to achieve their goals.

-Best Defense Against Spear Phishing, FIreEye

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Phishing emails are exploratory attacks in which criminals attempt to obtain victims’ sensitive data, such as personally identifiable information (PII) or network access credentials. These attacks open the door for further infiltration into any network the victim can access. Phishing typically involves both social engineering and technical trickery to deceive victims into opening attached files, clicking on embedded links and revealing sensitive information.

Spear phishing is more targeted. Cyber criminals who use spear-phishing tactics segment their victims, personalize the emails and impersonate specific senders. Their goal is to trick targets into clicking a link, opening an attachment or taking an unauthorized action. A phishing campaign may blanket an entire database of email addresses, but spear phishing targets specific individuals within specific organizations with a specific mission. By mining social networks for personal information about targets, an attacker can write emails that are extremely accurate and compelling. Once the target clicks on a link or opens an attachment, the attacker establishes a foothold in the network, enabling them to complete their illicit mission.

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A spear-phishing attack can display one or more of the following characteristics:

• Blended or multi-vector threat. Spear phishing uses a blend of email spoofing, dynamic URLs and drive-by downloads to bypass traditional defenses.
• Use of zero-day vulnerabilities. Advanced spearphishing attacks leverage zero-day vulnerabilities in browsers, plug-ins and desktop applications to compromise systems.
• Multi-stage attack. The spear-phishing email is the first stage of a blended attack that involves further stages of malware outbound communications, binary downloads and data exfiltration.
• Well-crafted email forgeries. Spear-phishing email threats usually target individuals, so they don’t bear much resemblance to the high-volume, broadcast spam that floods the Internet.

White Paper: Spear-Phishing Attacks, FIreEye