A 31-year-old UBS trader has been arrested in London for an unauthorized trading, which has cost Swiss banking giant UBS an estimated loss of 2 billion US dollars. 　　UBS shares have tumbled 11 percent at one point, after the news was announced. Meanwhile, the bank has stressed that client interests were not affected by the incident. The fraud may be the third-largest loss of its kind in banking history, and may also lead to a significant loss for UBS in the third quarter of 2011.