The Justice Department on Thursday filed a civil suit against UBS over “catastrophic” losses incurred by investors from mortgage-linked securities sold in the run-up to the financial crisis in 2006 and 2007.

The lawsuit, which UBS has vowed to fight, will likely leave a legal cloud hanging over Switzerland’s largest bank for many months. It also serves as a reminder that, more a decade after the collapse of Lehman Brothers, some of the issues at the heart of the financial crisis have yet to be fully resolved.