Web-server compromise is the unauthorized control of a public-facing server. Once attackers gain that foothold, they can change web content, plant redirects, steal credentials, install backdoors, or use the server as a launch point for further abuse. Because the server is exposed to the internet, compromise can affect many users at once and may be hard to notice if the site still looks normal.
In cyber security, this matters because trusted web infrastructure carries reputation as well as data. A compromised government, school, or business site can be used to host fraud pages, serve malicious scripts, or funnel visitors to phishing and gambling campaigns. Defenders look for unexpected file changes, new accounts, unusual outbound connections, web-shell activity, and integrity drift between the live site and the approved source code. Strong patching, least privilege, file integrity monitoring, and log review are key controls.