Autocad hack – Similar to Old Pharma hack?

This is regarding the web site https://www.infrastructureusa.org, currently using WP 3.8.3

Google just contacted me saying that my site was probably hacked, and sure enough they found a spammy URL attached to my site (touting AutoCad Autodesk). Weird thing is, I can’t find that file anywhere, nor can I find any evidence of malicious code or spammy content anywhere in my site files. The front end also seems completely clean and functional.

I found that when I do a site: query in Google for “Autocad” I come up with hundreds of spammy page descriptions–but when I search for individual page titles of pages that had spammy descriptions in a regular Google search, I get the pages with normal descriptions in the results. Any ideas what that could mean?

This whole things seems a lot like the the old “Pharma” attack from a few years ago (https://www.ads-software.com/support/topic/pharma-hack?replies=12) but I’ve followed all advice and just haven’t been able to find any suspicious looking files in the same locations or with the same filename format.

Anyone get the same hack, and hopefully find a solution?