Packet sniffing is a technique used to capture and analyze network traffic, which can include intercepting passwords while they are in transit.

When data packets are transmitted over a network, a packet sniffer can capture these packets, and if they are not encrypted, it can read sensitive information like passwords.

The other options:

Buffer overflow is a type of attack that exploits a program's memory handling.

Phishing is a social engineering attack to deceive users into providing sensitive information.

Black hat refers to a hacker with malicious intent, not a specific technique.

Therefore, packet sniffing is the correct technique for obtaining passwords in transit.