The Usage Checker shows I had a massive spike in download traffic over a 48-hour period earlier this month - about 20Gb, roughly 40x my normal daily traffic. As a result, my 20GB cap has well and truly blown.
I haven't been able to trace any downloads of such magnitude on my system. Any suggestions as to how I can monitor traffic in detail? Helpdesk have given me daily download figures, and confirmed that the unexpected activity is all Download, not Upload, but of course cannot give me connection logs or suchlike useful stuff. It's possible that the 20Gb comprised continual small transfers of data rather than one single file - based on the fact that I can't find any huge files anywhere on my system.
Tech SPec - Linux PC, wired link to Hub 5, Infinity Fibre 38Mb, wireless disabled, only system on router, no possibility of system use by persons known or unknown apart from me,