The Securities and Exchange Commission says its corporate filing system was hacked last year and the intruders may have used the nonpublic information they obtained to profit illegally.

The disclosure comes two months after a government watchdog said deficiencies in the agency’s computer systems put the information they contain at risk. It also follows a massive hack at the credit reporting agency Equifax.

The SEC issued a statement late Wednesday that said the breach was discovered last year but the possibility of illicit trading was only discovered last month. The statement did not explain why the hack itself was not revealed sooner.

The SEC files financial market disclosure documents through its EDGAR system, which processes over 1.7 million electronic filings in any given year.