Our webmaster tools account is showing 250.000 errors related with weird links from other sites.

These URLs are comming mostly from non existent sites or are being generated directly by our website.

Here some examples of these URLs:

oursite.com/&q=videos+caseros+sexo+pornos+gratis&sa=X&ei=R638T8eTO8WphAfF2vG8Bg&ved=0CCAQFjAC%2F%2Fpage%2F2%2Fpage%2F3%2Fpage%2F4%2Fpage%2F3%2Fpage%2F4%2Fpage%2F3%2Fpage%2F4%2Fpage%2F5%2Fpage%2F4/page/3

Our site is a popular spanish adult site, yet we don´t have keywords which are being mentioned in this URL. Apparently this link comes from our site.

Some more examples:

oursite.com/&q=losmejoresvideosporno&sa=X&ei=U__8T-BnqK7RBdjmhYsH&ved=0CBUQFjAA%2F%2Fpage%2F2%2Fpage%2F3%2Fpage%2F2%2Fpage%2F3%2Fpage%2F2%2Fpage%2F3%2Fpage%2F4%2Fpage%2F3%2Fpage%2F2%2Fpage%2F3/page/4

Once again: not our queries, not out URLs.

oursite/tag/tetonas

We think that it might be other site, which is having a policy of extremely bad SEO based on other sites branding and keywords usage:

thirdsite/buscador/tetonas-oursite

The question is: if other sites are generating these URLs, how can we prevent this?

Why the tag is being generated if no link was added to the other site?

What should we do with these errors? 301? 410 gone?

I have read all similar Q&A here but none of them seems to solve our problem. It is not likely to be a bad ad (Inspected them all). Maybe some all content which google decided to recrawl suddenly? Maybe third parties bad SEO policy? Maybe all of them?