Humbug Labs is an online service that can monitor your Asterisk CDR records and generate e-mail/SMS alerts based on predefined traffic patterns.
There are quite a few different types of alerts and you should spend a few minutes selecting the alerts that are relevant to your PBX system. Statistics are available free with Humbug Labs, and fraud alerts are available for a small monthly charge, based on your monthly call volume.
If a fraudster does figure out a way to place unauthorised calls through your phone system there’s a good chance they will place as many calls as they can, as quickly as possible. This can be a problem with VOIP as you may not have a limited number of ‘channels’ as you do with traditional phone systems.
Humbug Labs includes an alert that will send an e-mail/SMS if your system is used to place more than a predefined number of calls in an hour. It can also monitor the duration of all the calls placed in an hour.