What is the ruling on benefiting from the money of a brother who works in governmental security institutions that rule by other than the Sharia of Allah and contain many abominations, and what is the description of Salatul Khawf (the Prayer of Fear) in guerrilla warfare?

Benefiting from money is a branch of the ruling on acquiring it. If it was lawful (halal), then benefiting from it is lawful. If it was unlawful (haram), then it is forbidden. If it was mixed, it is disliked (makrooh). The ruling on acquiring it is related to its nature and effect. Thus, one who works in security institutions and helps an oppressed person or deters an oppressor is not equal to one who works in them and assists in injustice or participates in corruption.