reply to mahohmei
Re: Suddenly gobbling up data Have you tried to turn off or disconnect everything except the modem and see if your usage drops? Turn one device on at a time to see what's the bandwidth hog. That includes the WiFi as well; when turning it back on, don't connect anything to it.
Just because you don't have spyware and your PCs aren't glitching like Windows ME, doesn't mean that you don't have some sort of malware. Plenty of malware go unnoticed and run for a long time before they're discovered. Also, there may be an app that you've forgotten about that's hogging data; if you're running Windows, Task Manager will let you know the NIC interface utilization and may provide a hint on where to start looking.