First hour
Confirm and contain
- Isolate affected machines from the network. Leave them powered on so memory evidence survives.
- Start an incident log: time, who, what was seen, what was decided. Keep it from minute one.
- Move incident talk to a channel the attacker can't read: phones or a separate chat, not company email.
- Name one incident lead who makes the calls, and a deputy.
- Disable accounts you know are compromised and revoke their sessions, tokens and keys.