Precursor is correct.

Systematic probes across multiple host ports are reconnaissance actions that attackers use to map targets and find open services. That kind of activity is a classic Precursor because it happens before exploitation and it signals preparatory intent rather than proof of a successful breach.

IoA is incorrect because indicators of attack generally describe behaviors that show an attack is in progress such as exploit attempts, privilege escalation, or lateral movement. Port scanning is preparatory reconnaissance and is more appropriately labeled a Precursor than an ongoing attack indicator.

Indicators of Compromise (IoCs) is incorrect because IoCs are artifacts left by a successful compromise such as malicious files, altered system artifacts, or confirmed command and control traffic. A port scan alone does not demonstrate that a system has been compromised.

Indicator is incorrect because it is a generic term and not the specific taxonomy term used for preparatory reconnaissance. The correct, specific category for scanning activity is Precursor.

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