Toll Fraud / DOS attack help

Hello all, I seem to have been having a strange issue with my current voip setup. I am using bluebox and recently whenever my voip phones get incoming calls, they appear to be coupled with randomly generated outbound calls. This makes it almost impossible to use the phones. If anyone has ran into something like this before and has any experience resolving it, any help would be greatly appreciated. Thanks!

The world is full of scripts that search the internet for poorly secured IP PBX-es. It sounds to me that you have to beef-up your security on your IP PBX. If not urgent, make the PBX SIP port not available from the internet. If the PBX is available on the internet (SIP port), use a firewall to restrict possible attacks.