Check out the following article. It states that over 200,000 voice phishing/vishing calls into Korea, from other countries, were blocked in January and February. Some additional statistics are given as well that break the calls down by type, bank, etc. Most of them are imitating Korean banks. Unfortunately, there isn't any information about how these calls are blocked, I presumably by Korean service providers.
It seems like US-based service providers could do the same thing - block international calls claiming to be US-based finanical institutions. This isn't trivial though, you need technology at the right location in your network and managing blacklists of numbers takes a ton of work (I know, we do it too).
SecureLogix put out a press release for my new book, Hacking Exposed:UC and VoIP. The press releases includes a video summarizing the book. I posted a link to the video a few weeks ago, but it is here as well.
Here is an interesting report on a variety of fraud issues. One thing that struck me is that voice has become the preferred channel for fraud. Voice SPAM, scams, vishing, social engineering into contact centers, etc. Voice used to be the most trusted communications medium, but now it has become the LEAST trusted. Public voice has a ton of issues - is it any wonder that users are moving to closed systems for voice and messaging???
The Messaging, Malware and Mobile Anti-Abuse Working Group (M3AAWG) is holding a special interest group in their annual conference in San Francisco, February 17-21, to focus on issues unique to voice. This includes Telephony Denial of Service (TDoS), robocalls, voice SPAM, voice phishing, etc. I will attend and be on the solutions panel. Here is a link to an article discussing the special interest group.
Here is a bulletin from the FBI warning about toll free, 1-800 call pumping attacks. The basic idea (I cover this extensively in my Hacking Exposed: UC and VoIP book) is that the attacker, usually an unscrupulous service provider, generates many (perhaps millions) of calls into 1-800 numbers. They profit because they receive a piece of the 1-800 revenue, which is paid by the owner of the 1-800 number. See the bulletin below:
There are two types of attacks, one will "spray" many numbers with very short calls, in order to get a piece of the connect time revenue. Another will generate long calls, usually to a smaller number of 1-800 numbers and IVRs, in order to get a piece of the connect and per-minute charges. The latter form may require some analyis of the target 1-800 IVR, and use of tailor audio which dwells in the IVR through use of menu-looping DTMF tones or other audio.
Either type can generate a TDoS condition, if the attacker generates too many calls or if the calls target a part of an IVR or enterprise with limited bandwidth. This is especially true for calls which dwell in the IVR, because they consume more resources.
See the link below - Dancho Danchev who has blogged extensively about Telephony Denial of Service (TDoS), lists this issue as the #2 cybercrime trend for 2013. I agree and we are likely to see it grow in 2014.