OPM hack: 21 million people's personal information stolen, federal agency says

• OPM background check applicants since 2000 'highly likely' to be affected
• Office of Personnel Management computer networks infiltrated in late May

Sensitive information including social security numbers concerning more than 21 million people was stolen last month when the Office of Personnel Management (OPM) was hacked, the US federal agency said on Thursday.

OPM launched a "forensic investigation" after discovering that its internal database, housing background-check records of current, former and prospective federal employees and contractors, had been hacked in late May.