Is selling and maintaining computers forbidden, based on the noble verse: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression"?

If a person does not know, or does not predominantly assume, that something will be used for what is unlawful, then there is no sin upon him. The ruling of prohibition is not based on doubts, but on certainty or predominant assumption. The default is safety from what is unlawful, and one does not depart from this default except with strong evidence.