We built a new website for a client. When I do 'site:clientswebsite.com' in Google it shows some of the real, recently submitted pages. But it also shows many pages of spam url results, like this 'clientswebsite.com/gockumamaso/22753.htm' - all of which then go to the sites 404 page. They have page titles and meta descriptions in Chinese or Japanese too. Some of the urls are of real pages, and link to the correct page, despite having the same Chinese page titles and descriptions in the SERPS. When I went to remove all the spammy urls in Search Console (it only allowed me to temporarily hide them), a whole load of new ones popped up in the SERPS after a day or two. The site files itself are all fine, with no errors in the server logs. All the usual stuff...robots.txt, sitemap etc seems ok and the proper pages have all been requested for indexing and are slowly appearing.  The spammy ones continue though. What is going on and how can I fix it?