The personal data of 31,150 mostly former Optus customers was posted on short-term job website Freelancer.com in major breach of their privacy, Crikey can reveal.

Earlier this week, Crikey reported that an employee of the telecommunications company's debt collector ARC Mercantile had posted a spreadsheet of data of customers who owed a debt to Optus onto Freelancer.com, a job auctions website where potential workers bid to undertake a variety of short-term jobs or tasks.