some 17 billion of riskier credit suisse bonds were written down to zero as part of its emergency takeover switzerland’s move to wipe out 17 billion of credit suisse group ag bonds has prompted investors to reassess a market integral to the safety and resilience of europe’s banking system the credit suisse bonds that were written down as part of its takeover by ubs group ag were known as at1s or additional tier 1 bonds these instruments exploded in popularity in europe over the past decade and were seen as a way to build buffers that could protect banks in times of trouble without having to tap taxpayer funds