High CPU usage and outbound traffic

I have recently experienced high cpu + high outbound traffic (both at the same time) spikes. The process causing the high cpu usage is apache. I started looking through apache logs to see if I could spot anything weird. I didn't notice anything in particular.

Any thoughts to what might be causing this? Possible DOS? Someone simply using a download accelerator app? Is it possible for me to limit the outbound traffic/cpu usage per apache thread? I'm not much of an SA but would like some tips as to how I might be to figure out the root cause of these high cpu and outbound traffic spikes.

I have been using tools like htop, iptraf, tcpdump, etc. I guess I'm just hoping for some assistance from people who may have experienced similar issues and how they went about diagnostics and prevention. Thank you.