Of course everything that's electronic can be hacked, but there are enough checkmarks, atleast in India, to ensure that such hacking doesn't take place.
Manufacturer level hacking/foul play is eliminated with help of double randomization: first level which machine is going to be used in which constituency is randomly selected and second level where the position of each candidate in a constituency is also randomized. So, any foul play on the part of manufacturer or at the time of storage/transportation is simply not possible.
Now, once the machine reaches the booth and candidates are assigned, machines are tested in presence of all the candidates and can be used only if all give consent that the machine is working properly. After this, machine is kept in strict security. During elections, randomly some units are equiped with VVPAT, where there along with the electronic vote, the voter gets a paper confirmation of the vote and that paper confirmation is also stored in a safe box. No large scale discrepancies have been found while tallying votes from the machine and paper votes till now.
Of course there is still always a possibility that there are ways of foul play that I am missing, but at present I, in my capacity as an amateur political enthusiast and electronics engineer, don't think there is any reason to believe that EVMs are not giving correct results.