THE strange case of an undercover FBI agent, a senior Australian defence officer, a former White House adviser and a US investigation into money laundering in the Sudan came together with the soft chime of a Canberra door bell at 6.30pm last Thursday.

The bell rang at the home of a US citizen and Australian resident, Gwenyth Todd - a former Middle East adviser to the White House, the Pentagon and the US Navy - and her husband, a senior Australian Defence Force officer.

Gwenyth Todd ... alarm bells.

Ms Todd's husband answered the door and was greeted by a middle-aged man who said he was the US embassy consular officer Bill Phelps. He said that a recent incident involving Chinese hackers had compromised some US passports and he was warning local Americans.

Once inside the house he told Ms Todd - whose married surname begins with an H - he was speaking to US citizens with surnames starting with that letter.