What is the ruling on using open personal internet networks whose owner is unknown for personal or work purposes, and is work established through them considered void even if it becomes significant, like a relied-upon website?

It is impermissible to benefit from another's internet service except with their permission, because people's properties and honors are sacred (haram), and using them without the owner's consent is an aggression and a betrayal. If the state provides public networks, then it is permissible to use them. As for private networks, it is impermissible to use them except with the owner's permission, even if they are not password-protected. Whoever benefits from another's network without permission must seek forgiveness from its owner or pay him the value of what he benefited from. If it is impossible to reach the owner, then he must give charity equal to the value of the benefit on behalf of the owners and repent to Allah. There is no harm in benefiting from work completed via these networks, but rights must be returned to their owners.