An SBS 2008 server running on Hyper-V Core just ran out of disk space on the system volume. When I checked I found a 10GB Symantec Mail Security for Microsoft Exchange (SMSMSE or is that Information Foundation for blah blah) log file hiding in C:\Program Files (x86)\Symantec\SMSMSE\6.5\Server\logs.
I deleted it, but within a couple of minutes the free disk space had gone again. A scan of folder sizes using my old trusty dirsize.exe (and a second opinion from FolderSize) didn't show the culprit. The space had just disappeared. After rebooting the server and stopping the Mail Security services another log file appeared in the same directory.
Installed the latest version of SMSMSE (18.104.22.1688) but it was still a problem. Turned out to be corrupt virus definitions and corrupt spam rules (Brightmail)
Shut down all three SMSMSE services,
delete the VirusDefs0000000x folders from C:\Program Files (x86)\Common Files\Symantec Shared\definitions\AntiVirus
and delete the following from C:\Program Files (x86)\Symantec\SMSMSE\6.5\Server
- bm_ruleset folders
- .sequence.0 and .sequence.2
Then run Liveupdate with certified definitions from SMSMSE Admin Status page