Here is how it is detected:
We get that information from the log file in followed directory:
C:\Program Files\Trend Micro\OfficeScan Client\report\
There will be lots of files there such as
We use the time information of the recent log file.
I have one file in that directory: 20101022.log but my Last Virus Scan Date shows 6/3/2010 6:40:25 PM. My computer does show todays date for hardware/software scans.
This is our Security Suite detection method. Sorry, I will look into how we populate inventory.
There is a value in the registry and it can vary based on version. Along the same path that you are looking. Look for the value called "lastscantime" That is where it is pulled from.
Jason in tech support said it is checking HKLM\Software\TrendMicro\PC-cillinNTCorp\CurrentVersion\Schedule Clean, “LastCleanTime” but I don't have that in my registry.