I could use some help with Wordpress. When I do a site:mysite.com keyword search on Google, I'm getting hacked PDF links. Here's an example:

Search:
site:example.com prescription

Results:
example.com/add/tadalafil-prescription.pdf
example.com/.../finasteride-online-prescription.pdf
example.com/add/viagra-canada-prescription.pdf
etc... and they are many; over 10 pages of results.

However, all these links are broken. What I'm wondering is:

1. What's the likely Wordpress vulnerability that allowed this?
2. Could this be 'staged links' or the PDF files might actually have been there?