This is unfortunately untrue. If anything, recent times have shown that it is rather easy to take a majority vote in the network. (i.e. the network speed double

This is unfortunately untrue. If anything, recent times have shown that it is rather easy to take a majority vote in the network. (i.e. the network speed doubled in a mere 2 weeks, by a very limited increase in money spent for hardware). To decide if it's possible to cheat bitcoin you have to ask the question: How much money can I steal from people, how much money does it cost for me to steal from people. (and ofcourse how do I turn my stolen bitcoins in something valuable in a short amount of time). When the value of bitcoin is relatively stable as it is now, that's not likely, but when the value spikes (and outruns hardware investment cost) then perhaps there's a way to cheat.