The first thing that should be done when a SIEM flags a potential event is A. Validate the event is not a false positive. This is because a false positive is an event that is incorrectly identified as malicious or suspicious by the SIEM, when in fact it is benign or normal. False positives can waste the time and resources of the security team, and reduce the trust and confidence in the SIEM system. Therefore, it is important to verify the accuracy and validity of the event before initiating any further actions, such as incident response, escalation, or compensating controls. Validation can be done by analyzing the event data, comparing it with the baseline or normal behavior, and checking for any anomalies or indicators of compromise.
A false positive is an event that is incorrectly identified as malicious or suspicious by the SIEM, when in fact it is benign or normal. Validation can be done by analyzing the event data, comparing it with the baseline or normal behavior, and checking for any anomalies or indicators of compromise. (From CISM Manual or related resources)
References = CISM Review Manual 15th Edition, Chapter 4, Section 4.2.1, page 2091; CISM Review Questions, Answers & Explanations Manual 9th Edition, Question 72, page 19
