UBS AG posted an $18 billion loss for 2008, more than initially reported, and said it remains "extremely cautious" about the outlook for this year.

The full-year net loss widened by $1.03 billion from the figure reported on Feb. 10 because of costs to settle a U.S. tax investigation and additional writedowns on securities, the Zurich banking company said in its annual report, published Wednesday.

Peter Kurer, UBS' chairman, and Oswald Gruebel, its chief executive, said in a letter to shareholders that earnings will "remain at risk for some time to come" because the "balance sheet remains exposed to illiquid and volatile markets."

UBS agreed Feb. 18 to pay $780 million and disclose the names of about 300 secret account holders to avoid U.S. criminal prosecution on a charge that it helped wealthy Americans evade taxes. It also marked down securities that have not yet been transferred to the Swiss National Bank's fund as part of a government aid package following record losses.

The 2008 loss is the biggest in Switzerland's history. UBS has amassed more than $50 billion in writedowns and losses since the beginning of the financial crisis, forcing it to raise more than $32 billion in capital from investors — including the Swiss government — and cut 11,000 jobs.

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