Three Equifax investors sold $17.8 mln in shares days before the company announced it had suffered one of the biggest hacks in history.

As Reuters reports Friday, the shares sold three days after Equifax knew of the hack, and it was as yet “not clear whether these transactions were part of a pre-arranged sales plan.”

The credit giant has said that hackers gained entry to sensitive information from an unprecedented 143 mln accounts between May and July.

Data such as names, social security and driver’s license numbers fell into the hands of malicious parties, along with 209,000 credit card numbers.

Larger than any comparable attack in the US, Equifax is due to publish a report into the events in the coming weeks, while commentators highlight the vulnerability of centralized information storage.

“On a scale of 1 to 10, this is a 10,” an analyst told Reuters.

“It affects the whole credit reporting system in the United States because nobody can recover it, everyone uses the same data.”

Senate Select Committee on Intelligence vice-president Mike Warner went even further, describing the breach as “representing a real threat to the economic security of Americans.”

Legacy infrastructure is becoming an increasingly difficult topic to avoid as hackers launch ever more sophisticated attacks affecting hundreds of businesses and other organizations at once.

WannaCry, the Bitcoin ransomware attack which appeared in May, partly achieved its international success due to the inadequate and outdated software still used by prominent entities.