Possible hacking attempts

Hi all,
My phone lines are continually called by an automated system that seems to simply dial “9” for up to 6 minutes, then hangs up. On my IVRs, 9 is a language change, so the caller swaps IVRs continuously. I recently changed the IVR so that a second attempt to switch language is met with a hangup, but that does not seem to discourage them.

Lastly, the “caller” seems to be blocking caller ID (see log snippet below), so I can’t simply block the number. Over the course of a weekend, these calls can number up to 150. I have even logged a few occurances where the “caller” ties up two of my FXOs at the same time.

My questions:

  1. Has anyone else had this occur to them? Any idea what it is? My suspicion is that they are trying to obtain an outside line.
  2. Is there anything I can do to block this without affecting other calls?

[2013-04-29 08:26:23] VERBOSE[13851] sig_analog.c: – Starting simple switch on ‘DAHDI/4-1’
[2013-04-29 08:26:24] DEBUG[13851] chan_dahdi.c: CallerID number: (null), name: (null), flags=6
[2013-04-29 08:26:24] VERBOSE[13851] pbx.c: – Executing [[email protected]:1] NoOp(“DAHDI/4-1”, "Entering from-dahdi with DID == ") in new stack

If these calls are coming directly in on your PSTN lines as your post suggests, then it is unlikely a hacking attempt. To could turn on “Privacy manager” on your inbound route perhaps.

If these are really “nuisance calls”, then call your provider and complain, you might not have access to the underlying CID, but they do.