A SIEM alert is triggered due to unusual network traffic involving NetBIOS.

The pattern described most strongly indicates lateral movement: multiple network logons (Event ID 4624, Logon Type 3) across multiple machines in a short period, combined with NetBIOS/SMB-related service activity, suggests a host-to-host authentication pattern consistent with an attacker moving through the environment. In SOC terms, Logon Type 3 reflects network-based authentication (commonly SMB, remote service access, admin shares, or remote management). When the same source account or host triggers many network logons quickly across endpoints—especially outside normal administrative patterns—it often indicates credential abuse (pass-the-hash, stolen credentials, or remote execution frameworks). While SMB-worm propagation is possible, the scenario emphasizes authentication events across multiple machines rather than explicit malware indicators or file-write propagation patterns. Routine maintenance is plausible only with strong supporting context (approved admin accounts, change windows, known tooling), which is not provided. A single user connecting to shared files typically wouldn’t generate a burst of network logons “for multiple machines” in the same way, nor would it usually coincide with suspicious NetBIOS helper state changes as an anomaly. Therefore, the best classification is attacker lateral movement within the network.