What is the ruling on working for a telecommunications company that provides services—installation, modification, and maintenance—to usurious banks and insurance companies, whether these services are exclusive to them or shared with other institutions? And what is the ruling on providing an additional software service to colleagues, knowing that some of them provide services to the aforementioned entities? And will I be rewarded for this service?

It is not permissible to provide phone or internet services or similar to institutions based on unlawful dealings, such as usurious banks and commercial insurance companies, due to the prohibition of aiding in sin and aggression. There is no difference between installation, modification, or maintenance. If it is highly probable that your colleague will use the programming service for unlawful purposes, then it is not permissible to assist him. However, if the service is permissible and it is not known that it will be used for unlawful purposes, then there is no harm. Everything that is used for something unlawful or is highly likely to be used for something unlawful, its manufacturing, sale, and promotion are prohibited.