Oxfam has come under fire for failing to inform other aid organisations of the allegations against its staff including van Hauwermeiren, whose behaviour working for Oxfam in Chad had already led to complaints.
He went on to work for French charity Action Against Hunger in Bangladesh.
“We need to make sure anyone guilty of such gross misconduct is not able to move between different organisations, exposing more vulnerable people to risk,” said Byanyima.
Another man involved in the Haiti scandal was later hired by CAFOD, which fired him on Wednesday. The charity said it had received a reference from someone claiming to be his former Oxfam boss, sent from a private email account.
In response, Oxfam said it would create a global database of accredited referees to crack down on forged or unreliable references from past or current employees.