UBS trader in $2 billion loss on unauthorized trade

ZURICH (Reuters) - Switzerland's UBS said on Thursday it had discovered that unauthorized trading by a trader in its investment bank has caused a loss of some $2 billion.

"It is possible that this could lead UBS to report a loss for the third quarter of 2011. No client positions were affected," the bank said in a brief statement just before the stock market opened.

UBS shares immediately tumbled 8 percent.

(Reporting by Emma Thomasson)