from 200-600MB/day to 2-15GB/day.
At first i thought it was the typical reasons, unsecured Wifi/WPS, virus/rootkit on PC etc..
However after checking and ruling them all out we contacted the ISP (Telecom).
(We thought it might be someone else's usage getting crossed with theirs.)
The response back from telecom was...
This is the sixth case in the last week where people with Tenda modems notice this behaviour. With 4 of my cases we have proved the fault to the Tenda modem itself, and we're waiting back on information for the fifth case. Because of this I think there is a high chance in your case that the modem is also causing the issue. Do you have another modem (maybe an old Telecom one) lying around we'd be able to plug in for the time being to prove/disprove that the Tenda modem is at fault? Alternatively would it be possible to borrow a modem off a family member for one night so we could prove the same thing?
Complex Technical Support
There are likely many other people with Tenda modems with this issue and they may not even known it.
(I have informed PBTech of the issue)
So, if you have a Tenda W150D, or any Tenda. There is a potential security risk.
(It is still unknown what the extra traffic is.)