Someone who went to the same elementary school as Wonwoo (proof shots provided) connected the posts he left in their class's cafe to his Naver account and allegedly found a bunch anti SNSD posts he made when he was younger.
Comments such as:
"SNSD is the trash of the singing industry~!"
"Can't even tell who's who in this pre-plastic surgery photo of SNSD ㅎㅎ" (photoshopped pre-debut pictures of SNSD)
"ㅋㅋㅋ So much plastic surgery, the side effects of her plastic surgery causes her to flare her nostrils too big" (screencap of Sunny)
"Taeyeon's not afraid of antis it seems.. ㅎㅎ" (picture of Taeyeon with eyes and lips circled)
"Ow my eyes~~~" (on a picture of pre-debut vs post-debut Jessica)