I have encountered an interesting problem today.
I just happened to be looking at my site statistics and bandwidth usage, which normally tick a long at a few MB of bandwidth usage per month; accounting for the occasional visitor, me, and search engines.
Today it was a vast 6.1GB (!) for March so far, and rapidly nearing my 10GB hosting limit for a month.
Either I had a new found popularity, or something more sinister was at work.
Looking at the graphs the sudden upsurge had occurred in the last days of February, and was associated with two specific hosts.
Discussing this with my hosting company, we suspect the two IP addresses as hosting (whether they know it or not) comment-spam bots of some sort, that were trying to leave spam comments on my web site.
For some reason my comment system defences had got into an infinte deadlock with the spam bot, so that it was constantly re-trying.
It may be because I have a comment preview step first, which also shows the same filled in form, so that the bot was thinking that the submit had failed and was trying again.
I don't really know, but at the moment, all comments are disabled, and we are looking at blocking the IP addresses.
This is quite serious, because if they did exceed my 10GB limit, it would start to cost me a lot of money.