Sometimes customer get the spam message from the Short Dial Code (SDC) number. For example XL customer get SMS from 818 which give them information about prize or fake information. Most of the customer sure that the SMS was sent by the Customer Service, but it might sent from another operator.
Below is the picture of the Interoperator SMS – Message Termination (MT) flow to describe how someone can send the SMS.
For interoperator MT, customer can send MT by sending SMS to the SMSC directly to SMSC A. SMSC A the send request MAP-SEND-ROUTING-INFO-FOR-SM via GWMSC B and GWMSC B query to the HLR B to get the B# (target) location. HLR B send the VLR_ID of B# and send back to SMSC A. After knowing the location of B# (by VLR_ID), the SMSC A then send MAP-MT-FORWARD-SHORT-MESSAGE to GWMSC B and the GWMSC B will forward the SMS to the target (B#) via VMSC B.
From this call flow, I can give you an example how to check whether the SMS you’ve received are fake or not.
Someone (A#) send the MT from XXX SMSC (service center +3381835) to B# (XL number with service center +62818445009) whom have MSISDN +6281700001. He/she send MT by masking the sender into SDC 818 so that the B# think that he/she get SMS from the customer service.
The B# get SMS from 818 with content
“Selamat, anda memenangkan hadiah sebesar Rp.25 jt. Hubungi nomor 021-333333 untuk mengambil hadiah”
To check whether this SMS fake or not, you just see the SMS detail (hmm, I think this option only available for Nokia handset only). You check the SMS sender (818) and the service center / message center. If you see that the sender service center is +3381835, then the SMS is fake and bullshit :P, if the sender service center is +62818445009 then the information you’ve received is true (hoorray, you’ve got 25 million rupiah)