Some randomer got on stage and tried to pull Taeyeon off, he's been arrested now. Here, and he comes on around 3:37
SM said: “During the latter part of the event, there was an unexpected accident. Taeyeon, however, handled the matter bravely, and security staff prevented the situation from becoming more severe. At first, the audience and concert representatives all thought that a staff member was going on stage. After the concert, SNSD returned back to their dorms and are currently resting. We’re glad that the incident did not escalate into something more severe.”
Though, I don't know if I would be insulted if I was Hyoyeon, she was at the end and would've been easiest to take without the girls realizing?