What it is
Port scanning tools—such as nmap and masscan—probe network ranges to identify open ports and the services listening on them. Security teams use scanning for asset discovery and vulnerability assessment; attackers use it to map targets, fingerprint software, and prioritize exploitation. Scan techniques range from stealthy, slow probes designed to evade intrusion detection systems to high-speed sweeps that cover entire address spaces.
Different scan types (SYN, TCP connect, UDP, ACK) reveal varying levels of information. Combined with banner grabbing and service fingerprinting, port scans help attackers determine software versions, supported protocols, and potential CVEs to exploit in follow-up campaigns.
Why it matters
Detecting unauthorized scanning early can provide warning that an adversary is performing reconnaissance. Extensive scanning often precedes targeted attacks, giving defenders a chance to respond. Conversely, lacking visibility into scanning activity leaves organizations with limited opportunities to intervene before exploitation.
How to reduce risk
- Monitor network telemetry for unusual scanning patterns and alert on spikes.
- Deploy honeypots or deception hosts to detect reconnaissance actors.
- Reduce the attack surface by hardening exposed services and closing unnecessary ports.
- Rate-limit or geo-block suspicious scanning sources at the network edge.
- Conduct regular internal scanning to identify and remediate exposures proactively.