What technique involves gaining compromising information by observing someone from a close distance?

The technique of gaining compromising information by observing someone from a close distance is known as shoulder surfing. This method typically involves looking over someone's shoulder as they enter sensitive information, such as passwords or personal details, into a device. This type of observation can occur in various public settings, such as cafes, banks, or public transportation, where individuals are often preoccupied with their devices and may not notice someone watching them.

Shoulder surfing is particularly concerning because it requires no technological skills or advanced methods; it simply relies on physical proximity and attentiveness to capture sensitive data. The effectiveness of this technique highlights the importance of being aware of one's surroundings when handling sensitive information in public spaces.

The other options, while they involve different forms of deception or exploitation to obtain information, do not involve the direct observation that characterizes shoulder surfing. Phishing and spear phishing involve the use of fraudulent communications, often via email, to trick individuals into providing information, whereas social engineering encompasses a broader range of manipulation tactics that may not necessarily include the act of observation from close proximity.