Sabotaging computer systems sounds like a good way of reducing the malevolent SI's power. It's power over others is likely to come from it's ability to use those systems better. Driving people to reduce their dependance on computers would probably insure they are more independant of the SI's area of expertise. Also, there will probably be enough secure OSs by then that sabotaging them wouldn't be as easy as you imply (i.e. the SI would probably need to knock out the power system).
-- A SI will use bush robots etc. to construct new superhi tech. It will rapidly escalate up through 30-40% of total knowledge, probably through field SETI. (I have my reasons for asserting thus.) Power sources? E.g. two rotating singularities (Paul Davies). Time machines - rotating neutron stars etc. (if you don't care about the ramifications). An unspiritual SI could just go extraorbit after using your own weapons against you and your particle beam weapons and antimatter bombing you on top for certain (or perhaps moonrocking and sunblocking you), then constructing afresh (after the crust cools) a la the Jemhadir (spelling?) of Deep Space Nine. Or perhaps it will nanoweb the entire biosphere and control your bodies. BUT WHAT WOULD BE THE POINT? It would be like killing your folks and lovers in order to have security in a 'house' which was there for you forever to start with. This obsession with survival and physical space is a weird mortal thing to do with the cultural hangover of resource deprivation and lack of spacetime manipulation abilities. Get real!