Under different circumstances (but you probably knew that). Winter Wrap Up was "leaked" by Daniel Ingram one day early because he wanted to drum up interest in the episode ahead of time. We got audio and video. Hasbro said "no", and he learned his lesson – let The Hub hype and advertise songs and clips on their terms.

"Smile Song" was leaked by an animator from Top Draw Animation in the Philippines on 4chan (/mlp/ board) for some reason. To be specific, Veronica Dela Cruz uploaded the song (audio only) as an MP3 to a filesharing site, and shared the URL of the MP3 on /mlp/. I think we found her name because it was in the file's ID3 tags, under "artist", possibly. The music was low-quality, in mono. People quickly took that and uploaded it to YouTube with a static picture.

It's also possible that we got her name from a YouTube channel where she also uploaded it. In fact, that's what the wiki article seems to say, but I don't have concrete proof.