Originally Posted by k0nr4d

As was mentioned already - I recommend against anyone using any hosted javascript from a source that you do not trust 100%.

If someone were to embed a piece of javascript from my domain on theirs, and I could control and edit said javascript, I could:
- Steal your user's usernames and passwords
- Pop ads on your site
- Replace your ad urls with my own
- Steal your traffic while hiding any changes I made from your IP so it looks normal to you
- Pretty much anything I want on the user-facing side of your site.