SMBIOS is a structured table that BIOS/UEFI builds at boot and leaves in memory for any process to query. It describes the motherboard, CPU, RAM, chassis, and dozens of other entities of your machine.
What makes SMBIOS valuable to anti-cheats is that it's hard to fake on the fly. The table is filled in before Windows even boots, so user-mode utilities can't simply rewrite it without a kernel-level driver.
Inside SMBIOS live Type 1 (System Information) with UUID and serial, Type 2 (Baseboard) with motherboard serial, Type 3 (Chassis) with the asset tag, and Type 4 (Processor) with CPU identification.
Any HWID-changer that doesn't touch SMBIOS is essentially renaming the tip of the iceberg. The original UUID stays underneath, and any anti-cheat at the EAC or Vanguard level will see it.
We recommend always rewriting SMBIOS as a unit when changing HWID — UUID, baseboard serial, and chassis tag together. Otherwise you ship a Frankenstein profile with contradictory IDs that gets caught even faster than no spoofing at all.