We don't have that in our environment but have seem similar entries where warranty or refurb work was involved.  There is supposed to be part of the process of  a warranty motherboard swap where the serial number of the box is manually entered on the machine.  Seems some techs are ignoring or forgetting that part.

Thanks Brian, except we aren't using CMDB here, just CMS Level 1,so theres no way anyone could manually enter this info as yet.

Cheers Steve

yabru,
What Brian is talking about is using a vendor's (Dell, HP, etc) utility to "burn" the proper serial number into the system board after a replacement. 

Another possibility is that these systems are "white box" (non-branded) PCs with a "generic" motherboard in it (maybe a MSI, Asus, Epox, etc after-market/OEM motherboard).  Those systems typically can't be assigned a serial number unless the vendor provides a utility to burn one into the BIOS.

Hi you can check with the command:

WMIC BIOS

But the machines 01234567, and 00000000, are often "home made machines". UUID is also all 0.

So for this kind of PC, only MAC is allowed for PXE management, not TAG or UUID If you can identify the motherboard Model/builder, you can try getting the software for flashing your own serial, or change those 4 machines, probably a few obsolete. ;-)