Not just "dissidents," but religious minorities ...
Iran has an on-going, savage campaign of religious suppression, denying civil rights and judicial protections to their citizens who hold religious beliefs outside the state-sanctioned variant of Islam. Most egregious suppression, including seizure of property, exclusion from education, prohibitions against employment, denial of burial in any cemetery, imprisonment, mob-incited beatings, lynchings, and state-ordered death sentences, have accelerated in recent years against the fragmented Iranian Baha'i community. It is not surprising, then, that state-sponsored internet hacking would be conducted both within and without Iran as a campaign against that regime's perceived enemies.
A great fear of any repressive regime is the ability of the suppressed to find support and succor through the cracks of their prison walls.