The leak stems from the Transport Agency's hiring of IBM in 2015 to take over its IT operations.
IBM in turn used subcontractors in several Eastern European countries – making sensitive information as well as an entire database on Swedish drivers' licences accessible by foreign technicians who had not gone through the usual security clearance checks.
Although it is not known if it caused any harm, it is one of the largest breaches of government information in Sweden in decades, which may threaten the Social Democrat-led coalition as opposition parties have said they could put the issue to a confidence vote, and on Tuesday ministers were grilled by parliament.
Defence Minister Peter Hultqvist told a defence committee he had been told in March 2016 that Swedish security police Säpo were investigating Transportstyrelsen. "I got the picture that there were problems linked to outsourcing at Transportstyrelsen, that the security police and Armed Forces were in contact and that the Armed Forces were acting on it," Hultqvist was quoted by the TT news agency as telling Swedish MPs.
Transportstyrelsen's director general Maria Ågren, who agreed to bypass laws to speed up the outsourcing, was fired in January for undisclosed reasons at the time, but has since confessed to violating data handling and accepted a fine of 70,000 kronor (around $8,000), according to media reports earlier this month.
The decision to outsource Transportstyrelsen's IT maintenance was made a few years earlier with the former centre-right government at the helm, but the now-ruling centre-left coalition has been criticized for how it has handled the news once it emerged and how it has been communicated between ministers and to the public.
Opposition politicians on the parliamentary defence and justice committees on Tuesday honed in on reports that Hultqvist and Interior Minister Anders Ygeman knew about the suspicions in early 2016, but Infrastructure Minister Anna Johansson and Prime Minister Stefan Löfven were not informed until January this year.
Löfven has fended off criticism of poor communication between ministries, saying on Monday that it had been Johansson's job as infrastructure minister to inform him of Transportstyrelsen business, but that she had not been able to do so as she had not had that information herself, an explanation the opposition did not buy.
"(The fact) that a responsible minister didn't know what happened within her own field provides no confidence at all," Left Party leader Jonas Sjöstedt told TT on Monday.
Liberal Party MP Allan Widman, chairman of the parliamentary defence committee, said on Tuesday after the interrogation of Hultqvist that the government had shown shortcomings in how it handled the information.
"This is a serious flaw that has been exposed in this government. It does not work together, but everyone works in their own field and not together," he told TT.
Ygeman said he had informed the Ministry of Enterprise and Innovation (of which the Infrastructure Minister is part) when he was told by Säpo in 2016. Johansson has previously said her state secretary at the time failed to pass the information on to her. Ygeman added it had not been necessary to inform the Prime Minister at that point.
"This is not information you can talk about on the fika break or in the fika room; you have to be in special rooms to relay this kind of information. Information has been distributed to relevant ministries via the channels available to spread information between departments," he told the Aftonbladet tabloid on Tuesday.
Löfven was to meet all party leaders on Tuesday afternoon to discuss the incident.