Most companies run free trials before signing up and that's a perfect time to hit the prospect.

But will they put the trial code in example.com/index.php ?

How else will you find the signs of it?

Well I could tell what versions of Office software they were using by tracking these files for a company over time: Search Google for: site:starbucks.com filetype:doc

Doing an analysis of the files coming out of these companies could have a much wider appeal than just to what their website hosts too! If you can get them to go to your website, you can also glean an awful lot from their browser. There can be tons of legitimate reasons they might need to click on a link under your control, but as long as they do you also get what you need.