From the Daily Mail:
A mysterious round white object was filmed whizzing around a passenger plane above Seoul, the capital of South Korea, on April 7.
The clip, which has been uploaded to YouTube, begins with the ‘craft’ at the bottom of the screen, keeping pace with the passenger plane.
But then it speeds up and rises in altitude before zipping off out of shot, just as the startled person filming it tries to zoom in for a closer look.
What do you think it looks like?