It's Windows update, and it's slowly leaking memory, and it gets worse the longer your machine is up.
Usually starts to be noticeable after about 5-7 days of up-time.
Just happened again with one of the user machines I manage, was up 25 days, and Windows update was using 9.9 GB of the 8 GB of physical RAM (it was throwing memory exhaustion errors in the event logs).
I instruct my users to restart at least once a week which seems to stop the issue, but this user forgot...
Since this is the first question that pops up when you search for this
issue online I might add that restarting the Update Orchestrator
service will shut the process down cleanly and it will start out using
a more modest amount of RAM again
Humm... An "every few days" automated task scheduled that restarts the "Update Orchestrator service" may be a fix... will have to test :-)
I.e., in a CMD script which is run every 4 day via a scheduled task (credentials used would need to be admin)
net stop "Update Orchestrator service"
net start "Update Orchestrator service"