In iOS 10 Apple included the Invisible Ink feature which allows people to send obfuscated messages to and from iPhone and iPads. With this snippet by Darryl Huffman you can recreate that same text effect on your webpages.
When you hover over the hidden text it reveals the hidden message.
If you are having trouble with the pen, try the archived copy on GitHub
See the Pen
Invisible Ink | Mouse Over! iOS 10 by Darryl Huffman (@darrylhuffman)