Here is a link to a recent webinar I did back in March on Telephony Denial of Service (TDoS). We did this with one of our partners, iSight. The focus was on dealing with this issue in contact centers.
Check out our webinar on threats to contact centers.
I will be participating in a NoJitter webinar on October 10th, on the topic of Voice, VoIP, UC security in contact centers.
Here is an interesting article on contact center fraud.