The latest month of scanning has seemed valuable for the hackers. A Norwegian municipality has been hacked and their PBX has been calling Somalia and a lot of others destinations we have picked up on our VoIP honeypots during the last month.
If you have an unsecure IP PBX on the net, now it will only take hours before it will be detected. Most normal cause for this is misconfiguration. The people setting up the IP PBX has not taken security seriously and the IP PBX is wide open for calling.
The simplest ways is that inbound calls is routed out again if no local destination is found. A little harder is to just brute-force the password on extensions. I can only say, there will be more like this!
The hacker can sell this “gateway” to a third party dealing with calling cards. I have investigated frauds in Norway where they managed to send 1,2 million NOK (approx 200 000 USD) within 10 days. This was a Cisco installation, but misconfigured Asterisk installations are also abused a lot.