Revert multiple posts to an older revision?

Probably is a way with an SQL query.

But another solution is to use Search RegEx, which is a good plugin to be able to search and replace with grep and regular expressions through all posts and pages. And I’d delete all your revisions to make sure the links aren’t hidden in old revisions that might get restored at some point.

If you need to develop a regex search string to find spammy href links, check https://stackoverflow.com/questions/tagged/regex

And you can search for text strings with phpmyadmin in your Cpanel, or better yet, adminer, which is simpler and more secure. WordPress › Adminer « WordPress Plugins.