Too hard for me to work out as I only have a limited view of the stats. One way to get a guess would be to download the tickets file when it comes out and see all the accounts grouped together with almost the same number of tickets as they're likely to be botnets. My best guess is based on the fact there used to be 400 to 500 million tickets a week but now we're doing over a billion so I think 50% to 65% bots.
Maybe I'll make a graph out of that file and find out of they are all near each other or not (probably best).
... but they've switched to buying them instead. wetsuit said they're even depositing and buying tickets with the deposit to get around all the restrictions. Maybe if they have some bad luck and don't win anything that'll make think about not doing it next week.
Isn't that what you want, you're probably still then making a profit from them?
Restrictions on that are going to be really difficult to do as it'll block out a lot of regular users already.