# Is internal port scanning a sign of an intruder?

Often, unless you know who is doing it. Inside a company network there are a few legitimate scanners, such as a vulnerability scanner, an inventory tool, a network management system or a printer driver looking for devices, and they should be known, scheduled and documented. An ordinary workstation, a printer or a camera suddenly connecting to many internal addresses or many ports in a short time is a different matter: it is one of the clearest signs that someone is mapping the network after getting in, and it usually comes early, before the real damage. Keep a list of approved scanners and their addresses, so that an alert can be checked in seconds, and investigate everything else the same day. NetSenX flags scanning on every plan, Free included, including from devices that run no agent, when watched from a SPAN or TAP port.

FAQ: [Attack techniques explained](https://netsenx.com/en/faq/attacks) · https://netsenx.com/en/faq/is-internal-port-scanning-a-sign-of-an-intruder

## Read next

- https://netsenx.com/en/detect-lateral-movement-c2-beaconing
- https://netsenx.com/en/is-someone-inside-your-network

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