Account takeover, or ATO, happens when an attacker gains control of a legitimate user's account, usually through stolen or reused passwords, phishing, or malware, and then uses it as if they were the owner.

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‍Why it matters

Hijacked accounts are valuable because they already carry trust. A spam or scam message from a real, established account gets through where one from a new account might not, and the victim's friends and followers are more likely to believe it. The damage ranges from spam and fraud to the owner being locked out. One common route is credential stuffing, where attackers try username and password pairs leaked from one breach on many other sites, betting that people reuse passwords.

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‍Response and prevention

When a takeover is suspected, the usual steps are to lock the account, end active sessions, reset credentials, and help the real owner regain access, then remove anything the attacker posted. On the prevention side, multi-factor authentication and rate limits on login attempts do the most work against credential stuffing

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‍Signals that point to a takeover

Teams look for a login from an unusual device or location, a sudden change of email, password, or recovery details, and a burst of messages or posts that doesn't match the owner's normal behavior. No single signal proves it. Combined, they let a system flag likely takeovers early.