UBS AG updated the loss from its unauthorized trading scandal on Sunday to $2.3 billion from its previous $2 billion estimate, and also provided more details on how the alleged fraud was perpetrated.

“Before making a further announcement, we needed to be certain that we understood the positions that were booked and that we knew the amount of the resulting loss,” UBS said in a prepared statement released on Sunday.

UBS’s latest announcement came after it first disclosed about $2 billion in losses last Thursday, Sept. 15, by a trader in its investment bank. The incident could lead UBS to report a loss for the third quarter, the firm said last week.

The trader, Kweku Adoboli, has since been charged with fraud and false accounting in the United Kingdom. Adoboli was a trader at UBS’ London-based global synthetic equity business.

In its announcement on Sunday, UBS revealed no further information on how the loss from the unauthorized trading incident could affect third quarter results. UBS did provide more details as to how the unauthorized trading allegedly occurred.

In the past three months, unauthorized speculative trading occurred in multiple DAX, EuroStoxx and S&P 500 index futures, UBS said. While those positions were part of the normal business for a hedged portfolio in the firm’s global equity trading business, the full risk exposure was hidden.

“The true magnitude of the risk exposure was distorted because the positions had been offset in our systems with fictitious, forward-setting, cash ETF positions, allegedly executed by the trader,” UBS said Sunday. “These fictitious trades concealed the fact that the index futures trades violated UBS’s risk limits.”

UBS also said it has formed a special committee to conduct an independent investigation of the incident and the firm’s control environment. The committee includes David Sidwell, a senior independent director who will serve as chair reporting to UBS’s board of directors, as well as Ann Godbehere and Joseph Yam.