What is the ruling on working in scientific research to develop high-quality communication systems, knowing that they may be used for both permissible and impermissible purposes, and does the sin of impermissible use fall upon the researcher? And what are the jurisprudential rules related to that?

Telecommunication systems, such as phones and the internet, are used for both permissible and impermissible purposes. The general rule is that they should not be sold or provided to those who are known or strongly suspected to use them for disobedience, based on the Almighty's saying: (And do not cooperate in sin and aggression). Accordingly, if these systems are predominantly used for evil, then it is not permissible to assist in their development. Whoever avoids doubtful matters has cleared himself in regard to his religion and his honor, and due to the Prophet's (peace be upon him) saying: (Leave that which makes you doubt for that which does not make you doubt). Scholars have mentioned that it is not permissible to sell, manufacture, or maintain anything that aids in disobedience. Therefore, anything that is used in a prohibited manner, or is predominantly suspected of being so, is forbidden to manufacture, import, sell, or promote.