Its report said that attack would have meant a leak of customer information, an allegation that has not been denied by the firm, which says only a few customers were affected.

Deloitte apparently discovered the flaw in its computer system in March this year. But the hack could date from October or November 2016.

This act of computer piracy focused on the activities of multinationals from the United States. It is believed that the hackers entered via the email service with an administrator code. Deloitte has informed six of its customers that their data had been impacted by the attack.

Contacted by Paperjam.lu on 25 September, Deloitte Luxembourg said that the attack took place at the start of an email platform and that the affected platform is not used by the firm in Luxembourg.

Deloitte stated that it had put in place the necessary measures and conducted an inventory with the help of its own experts and external experts. It had contacted the competent authorities as soon as the incident was identified and each customer affected.

“The inventory allowed us to understand precisely what information was at risk and what the hacker actually did, and to determine that only a few customers were concerned. No disruption occurred on client files and the firm's ability to serve its clients,” Deloitte added, reiterating its commitment to keeping cybersecurity intact.