It is not required, but a majority of people who branched cyber were computer science (probably at least half of the 40 cyber slots), about 5-10 were IT/cyber science/ electrical engineering, and the rest miscellaneous other majors.
They might be increasing the slots next year, but this year were there 40 slots and the branch commandant managed to acquire 2 extra.
It is true that cyber comes with a 1 year ADSO, so you owe 6 years active minimum. If you BRADSO, you'll owe 9 years active. You also don't need to be at the top of the class -- that part is not true. People got cyber ranked well into the bottom half of the class. One of the most important things is the ability to demonstrate technical competence during the live interview.