It's a continuous process. People find ways to exploit the ranking algorithms, other people improve the algorithms, and so on, ad infinitum.
So, in a way, google should be thankful for these people?
Google would (probably) never have become so successful if it wasn't for SEOs and spammers
That's largely true because the SEOs and spammers were so successful at gaming Google's competition that the other search engines were all but useless when Google hit the scene.