The Progressive Conservatives and NDP chose the topic of the Social Assistance Management System for their lead question to the government in Question Period on Monday.
CBC News revealed the computer sent welfare recipients unauthorized direct deposits and cheques worth some $7-million dollars.
"Why are you going forward defending it? How much is this Liberal scandal going to cost us?" asked Interim PC leader Jim Wilson.
"The Liberals new program is causing chaos for clients and staff," said NDP leader Andrea Horwath.
Premier Kathleen Wynne says 99 per cent of the incorrect payments have been reversed. Indeed, the Liberals say the amounts from Friday have been drastically reduced and the problem has been fixed.
Wynne said the upgrade was necessary because there was an outdated system in place that needed to be upgraded.
The minister of community and social services responsible for the new automated system, Helena Jaczek, downplayed the problems.
"Clearly the opposition is trying to make a mountain out of a very small molehill," she said.
Government officials say they are still trying to collect some $300,000 in unauthorized payments.