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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.