Upon discovering a data breach, what is the best action for the analyst to take first?

In the context of responding to a data breach, the best action for an analyst to take first is to shut down the affected system. This immediate response serves to contain the breach and prevents further unauthorized access or data loss. By isolating the compromised system, the analyst can stop the attack in its tracks, limiting any potential damage and securing other parts of the network from being affected.

Restoring the system from backup would not be a prudent initial step because it does not address the root cause of the breach and could lead to a situation where the same vulnerability allows for a reinfection. Patching the affected system, while essential as a response to vulnerabilities, should not be the first action taken in the critical hours following the discovery of a breach. Before any remediation actions like patching or restoring from backup occur, it is crucial to secure the environment to prevent further damage while forensic analysis can be conducted to understand the nature of the breach.

Thus, the correct decision to shut down the affected system ensures immediate containment and preservation of evidence for further investigation.