I have a home wirelss modem now in the 2nd month of use. The log shows upto 500mb per hour usage at times when not in use ie. 2am-5am, and during the day when no-one is home. This amounts to 30-50Gb per month of my 200Gb allowance. Yes I can turn the modem off at the power - and nothing is logged. I am continuing to turn the modem off when not in use.
Yes, the security is fine - there are no unauthorised users. And No it is not phone and auto software updates (these are turned off) as suggested by Optus Support. I have seen similar posts on the Crowd query with no reasonable answer, except that the time logging is not accurate and this reflects general usage. In a month on Optus I have used 40Gb more than any usage over the last 5 years on my previous Bigpond provider. Where is this anonymous usage?
I had a similar situation a few years ago with a MobileBroadband SIM that was with my sister so I couldn't really tell what was going on so I brought it home and it didn't seem to be doing it. I trusted what my sister told me she was doing with the modem so I contacted Optus and they said they would repace the SIM which I couldn't see why especially since it worked OK at my house.
Anyway new SIM arrived and I activated it. I took it back to my sisters house and it worked fine for the next 3 years until she got NBN and didn't need it anymore. I can't garantee that the new SIM fixed it but the problem neevr occured again.
1/ If you know how to, go into the modem's settings and change your password. Then make the same changes to devices using the WiFi signal from that modem. Watch what happens over the days which follow. If there is no further mystery usage then you probably have some so and so of a person leeching your connection. It's rare but it can happen.
If you have teenagers in the house ask them if they've given out the WiFi password to friends so they can access the net whilst at your house. This is one of the common ways people end up leeching connections.
If you are prepared to stay up late to see who is using your service (if that's what's happening) then read the instructions here: