On December 30th, SISTAR heated up the stage of "2011 KBS Music Festival" with the performance of their hit song of the year "So Cool".

However, after the jaw-dropping stage, their stage costumes caught netizes' eyes and became the center of controversy. SISTAR wore short red mini dresses which feature skin-toned V-lines around the chest, giving off a almost-naked illusions. Members Hyorin and Bora also ended up exposing their underwear as they bent down side by side.

Surprised netizens commented, "I was so surprised during that part!", "I was worried from the start and then it happened" and "It seems they need to pay a little more attention to their outfits".