After talking with my webhost, we tracked the spike in my bandwidth usage to a group of IP addresses in 64.62.168.*. Upon further investigation, it appears one or more computers in that block of IP addresses is searching for some sort of vulnerability in various online forum software. Since I do run a small forum for a friend; I’ve blocked all access from that group IP addresses. This appears to have stopped the sudden bandwidth spike and kept this site from going down over the weekend.