I just read an article by Zach Aysan that should be very interesting to you if you pull from diverse sources to create online content. More so if some of those sources wish to remain anonymous.
An executive summary:
Zero Width Characters are real, they've been around for a while(warning: geek link) and can be nearly impossible to detect or eliminiate unless you hand-copy text by retyping it yourself; or use OCR on an image. It's possible the creator of the text may not know if it's present.
On the other hand if you create a lot of original content finger printing your own work could be very useful!
The original article can be found here.
And a followup here.