Attackers sometimes hide code away from prying eyes by URL Encoding it.
The purpose of URL Encoding is to allow non-URL compatible characters to be passed via the URL. There are many legitimate reasons for doing this, such as hiding email from spammers, dealing with spaces in file names. etc.
Here are some trivial, non-functioning examples of URL Encoded text:
|this line has spaces||this%20line%20has%20spaces|