You may have been hit with spam that advertises a URL that contains percent signs. Your efforts to complain may have been met with frustration because you can't figure out where to complain to. What you may not have realized, is that the percent sign means that the next two characters are to be taken as a number in hexadecimal (base 16, with the letters A to F standing for 10 to 15). This number is the ASCII code for the character that really goes there. What a royal pain to do by hand! But, how easy to do by computer! To see just how easy, check out p2a.java.
(I know this is ugly. Have patience; I haven't learned much about layout manglers yet.)