UBS lost $2.3B because one trader in London hid his positions with fake ETF trades

Kweku Adoboli, a trader at UBS's London office, built unauthorized positions in equity ETFs totaling approximately $23 billion — far exceeding his trading limits. He concealed the positions by entering fictitious offsetting trades in the bank's systems, creating the appearance of a hedged, low-risk book.

In September 2011, as markets declined, Adoboli's positions lost value rapidly. UBS discovered the unauthorized trades and unwound the positions, crystallizing a $2.3 billion loss — the largest rogue trading loss in UK history at the time.

Adoboli was convicted of fraud and sentenced to seven years in prison. The case exposed failures in UBS's internal controls: the fictitious trades were not verified, and Adoboli's positions exceeded his limits without triggering alerts. The case illustrated how a trader who understands the control system can exploit its gaps, and how the assumption that internal records are accurate is the foundation of every risk model.