Did your freehost offer FTP?
I once had a empty server standing, with freehost script installed etc. No
http:// was working on the server since it was never setup probably.
But suddently it was pulling around 20 mbit or so.
Turned out it was hacked and someone was sharing files on FTP or something. Lasted for aprox 24 hours as well.
So your box was probably hacked, there was no trace of any activity on my server neither since log files usually don't show FTP / Shell activity