What do you think this is?

HI there. I’ve had this big rise in CPU use on my server for the last couple of days, and not ever before. It seems related to mysql, but I don’t know why… I’ll post the graphs and see what you think. I’ve already looked at cron and there?s nothing strange or changed. As you can see, this is basically a web server, so there?s no email going in or out. Check the cpu spikes at 1600!. Thanks in advance!