[Gsmmap] Silent SMS recorded. What now?

oliver.ast at telekom.de oliver.ast at telekom.de
Mon Mar 2 23:24:54 CET 2015

Hi Quel,

one typical example for such a behavior is indeed the roaming scenario.

On most of the SIM cards used today there are fields defining preferred networks. The operator controlled PLMN list (OPLMN) is maintained and typically also updated by the home network operator over the air (OTA). This happens usually whenever you enter a new country. That way the operators can direct the devices to first try connecting to preferred partner networks in these countries. Even still today this information is typically send via binary SMSs directly to the SIM cards (invisible to the user). Theoretically it could be done as well via BIP (Bearer Independent Protocol) over a normal data connection but this is often not supported by legacy SIM cards. Depending on the size of the PLMN list that is being updated you may receive a different number of SMSs. In my scenario with Telekom Deutschland I always get 4 SMS that are then becoming visible in SnoopSnitch (verified recently three days in a row on the airports after landing when visiting different countries).

Most likely you experienced the same when travelling around and crossing borders :)



From: gsmmap-bounces at lists.srlabs.de [mailto:gsmmap-bounces at lists.srlabs.de] On Behalf Of Quel Con
Sent: Monday, March 02, 2015 10:36 PM
To: Ralph A. Schmid, dk5ras; gsmmap at lists.srlabs.de
Subject: Re: [Gsmmap] Silent SMS recorded. What now?

Hi Ralph,

Thanks for the reply. I was able to track down my approximate location the moment I received the silent SMS: I was likely crossing from Belgium into Germany. The SMS seem to have been sent from the Belgian network (source numbers) but I assume they have been linked to the roaming network switching at the border. And if Alex is correct, then I worry even less and rather monitor my phone when crossing the border next time... (-:

Thanks again for your replies!

From: ralph at schmid.xxx<mailto:ralph at schmid.xxx>
To: quelcon at outlook.com<mailto:quelcon at outlook.com>; gsmmap at lists.srlabs.de<mailto:gsmmap at lists.srlabs.de>
Subject: RE: [Gsmmap] Silent SMS recorded. What now?
Date: Mon, 2 Mar 2015 16:17:23 +0100
I do not know the inner workings of SnoopSnitch, but control messages also can come from a smart phone phoning home (BlackBerries are known for this) and causing an answer of the network, and it is possible that the provider configures the SIM remotely, what I have seen with O2 Germany quite often. Maybe the app catches such communication? What is your home network, and (if applicable) in what network have you been roaming?


From: gsmmap-bounces at lists.srlabs.de<mailto:gsmmap-bounces at lists.srlabs.de> [mailto:gsmmap-bounces at lists.srlabs.de] On Behalf Of Quel Con
Sent: Monday, March 2, 2015 3:18 PM
To: gsmmap at lists.srlabs.de<mailto:gsmmap at lists.srlabs.de>
Subject: [Gsmmap] Silent SMS recorded. What now?

Hello everyone,

I am a non-tech person with some user skills and have SnoopSnitch running since a couple of months. While driving a car somewhere on a European highway on Feb 27 in the evening, I received a warning for two silent ("binary") SMS that my cell phone received.

I would be very grateful if you could help me to better understand what is happening here:

- Does SnoopSnitch block those SMS or just monitor them?
- Is there anything I should/can do now?
- What kind of information could someone receive from me by sending me such silent SMS?
- Does that compromise my phone's security?
- Is the info that SnoopSnitch collects (cell ID, SMSC, source no.) valuable/helpful to anyone for analysis?

Thank you very much in advance for any help you can provide!

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