As a praxis, all external content on our site is put in iframes to lower the risks of any external parties injecting stuff to our users. We also do it to make sure our content shows up before banners, to make the site feel quicker.

We now have an external script running which we want to put in an iframe, but it does not have any visible content to go with it so I want to put css "visibility: hidden;" on the iframe.

I read in a forum somewhere that search engines will lower the rank of a page, or even drop the page, if a iframe has "the minimal size of 1x1px". 

Will a search engine lower the rank of my page if I have a hidden (or 1px big) iframe?