How long do attackers stay in a network before they are found?

Usually days to weeks, sometimes far longer. Mandiant's M-Trends 2026 report puts the global median dwell time, the time from the start of an intrusion to its discovery, at 14 days for the incidents it investigated in 2025. A median hides a long tail: half of those intrusions lasted longer than that. Dwell time is short when the attacker is noisy, as with ransomware, and long when the goal is quiet access or data theft, and intrusions that an outside party discovers have tended to run longer than those a company finds itself. What shortens it is someone watching behaviour, not only signatures: regular check-ins with a new outside server, scanning, new sessions between hosts. NetSenX flags those on every plan, Free included, on the segments it monitors.

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