A remote intruder wants to take inventory of a network so exploits can be researched. The intruder is looking for information about software versions on the network. Which of the following techniques

Banner grabbing involves connecting to a network service (such as FTP, HTTP, SSH, or SMTP) and reading the response header or banner that the service sends back, which often contains the software name, version, and operating system details. This information allows attackers to identify vulnerable software versions and research applicable exploits. It is a passive-to-active reconnaissance method specifically aimed at enumerating software and service information.

Port scanning identifies which ports are open on a host to determine what services are running, but does not inherently reveal software version information from service banners.

Packet sniffing captures network traffic in transit to analyze data, credentials, or communications, and is not specifically targeted at collecting software version information from services.

Virus scanning is a defensive technique used to detect malware on a system and is not a reconnaissance method used by attackers to gather network inventory information.