Port scanning
port scan · network scanning · service discovery · network mapping · balayage de ports
A technique that probes a machine’s network “doors” to find out which ones are open and which services answer behind them.
In practice
Every exposed service (website, email, remote access, database) listens on a port. A scan lists these services, often with their versions: it is the map that is then used to look for known vulnerabilities. Bots sweep the entire internet constantly, so a service exposed by mistake can be found very quickly. Scanning your own addresses is good practice; doing it to other people’s systems without authorisation is not acceptable.
Fictional case: a contractor opens remote desktop access on a server for maintenance, then forgets to close it. Three weeks later, ransomware comes in through that door, found by an automated scan. A monthly scan of the company’s own addresses would have flagged it in time.
How to protect yourself
- Scan your own public IP addresses regularly and compare what is exposed with what should be.
- Close everything that is not essential at the firewall by default, and never expose administration directly (remote desktop, SSH, databases).
- Put remote access behind a VPN or a zero trust access solution, with MFA.
- Have scans detected by the IDS or the SIEM: they are often a sign of reconnaissance.
