Big data and data science is not just for good guys. If properly leveraged, it also provides competitive advantages for criminals, over their competitors, or to avoid detection.
Traditional Botnets (used for spam, phishing and other crimes) require a large network of infected machines to work. With better data science capable of identifying these zombie machines and shutting them down, spammers have found a new solution. This new solution is also less illegal as it relies on real email accounts that they own.
So how do they do it on a large scale? They open millions of accounts on Gmail, Yahoo and especially Hotmail. To open these accounts, they use automated web robots deployed in an highly distributed architecture, possibly using a traditional Botnet.
I know this because they actually resell these accounts. Once you have purchased 10,000 of these verified Yahoo email accounts for $100 on Bulkaccounts.net, you receive the list of logins/passwords in a spreadsheet, and now you can start sending your spam. You will need another web robot to log on automatically on all these accounts, compose a message and then get it sent out - but it's easy to find a hacker working remotely oversea and paid via Paypal. I'm assuming that after a few hundred messages per account, these Yahoo accounts will be terminated, but in the meanwhile, they have offered the criminal a possibility to massively deliver his payload - typically spam messages with links to get your computer infected, turned into a bot, or get your personal info stolen.