blocking people registering 'subscribers'

just been spending all day trying to sort out the hacked by ghost-dz, ive noticed ive had alot of so called registered subscribers very few personal emails alot of junk which is causing a problem, i was wondering how i can prevent any tom, dick or harry registering in 3 days i got 3,500 users since i dont know what to do plus I use the theme ‘sight’ but for some reason most of the side bar plugins graphics all seem to be at the bottom of the page rather than the side panel, i havent a clue why, i had one possible reason is alot of theposts are for trailers and when i changed theme the trailer size was different alot bigger. any clues will be good