why put smiley face defaced my website?

What’s with the smiley face at the very bottom of my pages about? I traced it back to this plugin after stressing and worrying for a week it was a hack. Why do this? and why not disclose you do this? Pissed me off big time. A lot of people put a lot of hours into their sites and you play these games with pissy little hidden code!!! I’m glad I deleted this plugin, useless and then you go and graffiti my fence!! You lost trust by this big time. Anyone considering this plugin,…who knows what’s in this from this shifty, shaded mob. Good ridence!!