Two more ex-Madoff employees have been sentenced to prison for assisting in the multi-billion dollar ponzi scheme.

Bernard Madoff's longtime assistant, Annette Bongiorno, was sentenced to a six-year prison term, while his former computer programmer, Jerome O'Hara, received 2.5 years.

Bongiorno became a multimillionaire after joining Madoff's company at the age of 19 as a personal secretary. She blindly obeyed her boss, and failed to recognise the fraud that happened "right in front of her," according to US district court judge Laura Taylor Swain.

However, Swain said that Bongiorno was not fundamentally corrupt and could not be described as a "coldly calculating, knowing participant" in the fraud.

"She was a pampered, compliant and grossly overpaid clerical worker," according to the judge.

Her sentence was lower than the more than 20-year term sought by prosecutors.

She had been convicted last March of conspiracy, securities fraud and other charges, along with four other Madoff associates.

Sentencing O'Hara, the judge said his actions "kept in place the essential backbone of the infrastructure" that perpetuated the fraud.

Other Madoff employees convicted in March are former back-office director Daniel Bonventre, computer programmer George Perez and portfolio manager Joann Crupi.

Fifteen people have been convicted so far in connection with the fraud, which is estimated to have costed investors more than $17bn (£10.9bn, €13.8bn).

Madoff pleaded guilty in 2009 and was sentenced to 150 years in prison for controlling the biggest Ponzi scheme in history. His brother Peter Madoff pleaded guilty in 2012 to his part in the fraud and was sentenced to 10 years in jail.