The name of this four member girl group is Secret (시크릿). They were formed by TS entertainment and their members are Hyo Sung (효성), Zinger (징거), Ji Eun (지은), and Sun Hwa(선화). They debuted in 2009 but have made it big in the summer of 2010 with the help of their two big hits, Madonna (마돈나), and Magic (매직).
I know this video makes no sense, and is a complete rip off of a Beyonce song, but it is still enjoyable.
The other song I did not like as much, but was a bigger hit. So here it is as well.