The Government Gateway was shutdown after a memory stick containing user names and passwords for the wed site that gives access to everything from tax returns to parking tickets, was found in a pub car park.
Ministers ordered an emergency shutdown of the Atos Origin-run site and ordered inquiry into this latest data security debacle.
The Department for Work and Pensions said the memory stick contained user names and passwords for testing an old version of the system and may not hold details of members of the public.
"We have moved immediately to make sure there is no conceivable risk to users of the Government Gateway, and are convinced the integrity has not been compromised,” a DWP representative told the Press Association.
"On the basis of an initial examination of the contents of the memory stick, it is our experts' opinion that the contents would not allow anyone to breach the very strong security safeguards protecting the website."
However, “strong security safeguards” have, time and again, proved inadequate to the task of securing personal data in both the public and private sector.
Commenting on this latest incident, Atos Origin said that an employee had removed the memory stick from the company's premises in "direct breach" of its operating procedures.
The government’s Information Commissioner last week said 277 incidents of data breaches had been reported to his office this year.
Eighty of those breaches concerned the private sector, 75 within the NHS and other health bodies, 28 reported by central government, 26 by local authorities, and 47 by the rest of the public sector.
But Thomas also noted that the amount of data breaches that have been reported to the ICO is might "still be well short of the total".
In the past year, the ICO has taken enforcement action regarding data losses against HM Revenue & Customs, the Ministry of Defence, the Department of Health, the Foreign and Commonwealth Office, Virgin Media, Skipton Financial Services, Carphone Warehouse, TalkTalk and Orange.