This question involves a situation where somebody might possibly be misusing a relative's mobile phone to discreetly engage in some questionable online activity.
Sharing of mobile devices is still common here in India and is quite the accepted practice in many offices and families.
A sim card registered to my friend A is currently used not by her, but other family members including her mother for various routine tasks including online shopping and email, and by her brother B who is the primary user, mainly for internet browsing and listening to music. His cousin C (father's brother's son) also "borrows" the phone regularly, which is impossible to refuse without offending close relatives in this joint family.
Cousin C is a college student who has recently fallen in with bad company and my friend B is now apprehensive that his cousin may be misusing the device to engage in some questionable online activities, being cunning enough to avoid directly exposing his own name, mobile number or email id. He might be doing this using either browsers or simple sms, which do not record which person is actually making use of the mobile device.
I have strongly advised B not to allow the cousin any further access to the phone, even at risk of unpleasantness within the family, but if his cousin had already infringed the law (strictly hypothetical, since we have no proof he has done so) will the responsibility fall upon my friend A solely for being the registered owner of the sim, or upon her brother B for being the primary user, when there is no other indication that either of them have actually participated in such an activity? Specifically, how can A and B defend themselves without blaming C when there is no conclusive evidence against any one of them being the guilty party?
Research done: I have tried to take advice from various websites devoted to questions on Indian law such as those listed in ask law india google search but found that most of them will only answer to an actual legal problem and refuse to allow such hypothetical or 'academic' questions, unlike Law Stack Exchange.