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For some time, I'm called several times per day by the same phone number. If I answer the call, the line is completely silent. On only one occasion I heard a standard "elevator music". No matter what I say or don't say, the line remains silent. If I don't disconnect, then it disconnects itself automatically after exactly 1 minute.

I did a google search for this number, and discovered forums where many people report the exact same thing I described above. Most say the line is silent, a few say they hear a generic telemarketing text about some medical products or a job offer. I never called it back, but those who called it back report that no one answers, they hear generic elevator music ad infinitum, or a robotic voice tells them the call is restricted.

Why I'm posting this here, is because I'm curious whether this can be an attack vector, or if it can have some other nefarious purpose. A telemarketing call I can understand, but to call and not say anything, probably do it for a huge number of people, there has to be a reason they invest time and money in this scheme.

What purpose can such a scheme have?

  • trick people to call them back, and milk them via a premium number service? The number seems to be a perfectly ordinary landline number from the same country I'm in. Can such a thing be disguised?

  • To know which phone numbers are in use by people, so they can later sell this list to telemarketers? In this case, one call should have been enough, why make several calls per day for many weeks?

  • Phishing, hoping that people answer with their names or they blurt out other information about themselves, so they can build a list with names and phone numbers? I never say my name when an unknown number calls me on my private phone.

marked as duplicate by Lie Ryan, S.L. Barth, Rory Alsop Aug 15 '16 at 17:41

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  • If you want a list of phone numbers and names, there are plenty of number lookup websites that you could scrape. So I dont think its that. – Anders Jun 10 '16 at 6:24
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    "there has to be a reason they invest time and money" Your number might be an entry in their messy, cheap database, the cost of a single call might be zero in their package, and they might have a malfunctioning voice board in their server or a buggy system. It is equally likely that they don't want to invest time and money to fix things. – techraf Jun 10 '16 at 6:36
  • Unless you want to split your hair in 4, you normally should have no reason to worry about such a thing as the fact that the call gets answered or not doesn't even guarantee that there is someone there or not. – Julie Pelletier Jun 10 '16 at 6:42
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    "Never attribute to malice that which can be adequately explained by stupidity." – gowenfawr Jun 11 '16 at 16:37
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    While this could be anything in theory, in practice it's extremely likely it's just a badly configured robocalling server, especially if many people report the same thing. – André Borie Aug 13 '16 at 20:35
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Getting someone to answer a phone call tells you roughly two things.

  1. The number called is a valid, active number.
  2. The person answering is reachable at that number (and probably "on the phone" at the moment they answer the call).

The security implications of those two things can vary widely, from basically nothing at all, to literally life and death. That's enough information to kill someone with an exploding cellphone, for example. Basically, someone on the other end of the phone can ascertain that the number they dialed is valid, and that you're (probably) in close physical proximity to your phone. Depending on what other resources and information they have, they may be able to translate that into the physical location of you and/or your phone.

It's definitely plausible that this could be used for surveillance or location-tracking, either by law-enforcement or non-government organizations (having basic location data about you would be useful to someone wanting to burgle your home, for example), however, as noted in the comments, that's very unlikely in this specific case. In this specific case, what happening is that you're being dialed by a telemarketing operation that doesn't have either the resources or motivation to surveil or assassinate you. As mentioned in comments, this is probably just the result of a buggy or poorly designed setup - the best and brightest technical talent doesn't typically get into telemarketing for shady fly-by-night operations, and it may well cost more to fix than it's worth.

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