It was a huge dating scandal apparently. I think IU got a lot of hate from the BG's fans, i'm not sure if the BG member himself got hate as well. I dont know if the Korean GP cared or not, since obviously it didnt hurt IU's career.
WhyKnock why dont you give us all another history lesson here, i dont remember much about this story.
Eunhyuk has been ridiculed by all the Korean fans since then and he now only appears in variety shows produced by SM. Some ELFs have not forgiven the singer who took the photo to this day.