@Geddy, I went hunting and did indeed find the ud*.state files in C:\Users\{username}\AppData\Local\Temp. Went ahead and deleted them too.
Also increased java memory to 1024m. Thanks for that hint.
@Techman, if Norton can delete them, can I not do so manually as well? The /temp folder is close to 6GB! I used to have System Mechanic, which did do clean-up chores like this, but didn't bother install it on my new rig. maybe I should install it again.
Update: I used Windows Disk Cleanup, which includes deleting temporary files. All in all close to 8GB. Good riddance. And I enabled Windows Storage Sense, which will do this automatically in the future.
Thanks to both of you again.