"zclyz8p9.sis" is probably an symbian file (could be an virus for the older symbian os).
SE K320i,ASUS P750 and Moto V3i don't support symbian. So you will probably get an format not supported when you try to open the file.
As for ur bluetooth query, you can set ur bluetooth device as "Hidden" & use the Paired device feature for accepting connections from only the phones u have paired up with.
But i would suggest u to turn it off when not in use, as it will drain battery faster.
Charan note:
ASUS P750 is an win mobile, which installs files with "CAB" extension or more.
Is it possible to execute a file in win mobile if the files extension has been changed from "CAB" to "SIS".
If u didn't get what i am trying to convey here is for example if u rename an MP3 media file extension to SIS etc. and try to open the file then some media players still can play it.
If win mobile supports execution even if the extension is changed then be very careful as it can be an win mobile virus,
If not just use "Hidden" feature mentioned above.
And Charan if possible never accept any file from an untrusted source no matter how nice the incoming file sounds