The Committee found HSBC's lax procedures allowed it to be used to launder millions of dollars by Mexican drug cartels, the Saudi bank Al Rajhi (linked to Al Qaeda) and, in the face of international restrictions, the Iranian and Sudanese governments.
At the moment media attention in the UK is centred on Trade Minister Lord Green. An ordained Church of England Vicar who writes on business ethics, Green was Chairman of HSBC from 2003-6 and then Chief Executive until 2010, when he joined David Cameron's government.
Researchers such as Robert Pape have in the past pinned down that Al-Qaeda appears to be a mostly Saudi organisation. Al Rajhi bank, the Kingdom's largest financial institution, seems to have played a key role in the activities of the world's most infamous terrorist organisation. The executive summary of Carl Levin's senate report states:
In particular, HSBC has been active in Saudi Arabia, conducting substantial banking activities through affiliates as well as doing business with Saudi Arabia’s largest private financial institution, Al Rajhi Bank. After the 9-11 terrorist attack in 2001, evidence began to emerge that Al Rajhi Bank and some of its owners had links to financing organizations associated with terrorism, including evidence that the bank’s key founder was an early financial benefactor of al Qaeda. In 2005, HSBC announced internally that its affiliates should sever ties with Al Rajhi Bank, but then reversed itself four months later, leaving the decision up to each affiliate. HSBC Middle East, among other HSBC affiliates, continued to do business with the bank.
There is plenty more along those lines - but I encourage you to read Levin's report executive summary, and/or the report in full here.