The BBC learned that the hackers behind the cyber attacks of Marks & Spencer (M&S) managed to pass a third party access that could access their systems.

The cyber attack that occurred in April has resulted in millions of pounds of sales losses in M&S and has worked to get the service back to normal, with online orders suspended for more than three weeks.

The supermarket declined to comment on the violation or the nature of these new details, saying "the availability is now in a more normal place with good stores this weekend's stockpiles."

Dragonforce (the name the criminal is using) previously told the BBC that it was behind the attack, and was also responsible for hacking the cooperative and attempts toward Harrods.

M&S will announce its annual results on Wednesday, but the focus will be on the devastating attacks and their financial impact.

Bank of America analysts believe M&S has lost more than £40 million in sales per week since the incident began on the Easter Banking Holiday weekend.

It announced on April 25 that it has stopped accepting online orders. Some stores left empty food shelves after the company had to place some food-related systems offline.

Based on preventive measures, M&S decided to shut down many of its IT operations after an attack, effectively locking its core system when it worked hard to handle the attack.

The biggest challenge is to get its online system fully operational again, which accounts for about one-third of its clothing and household goods sales.

"Our stores are still open, with availability now in a more general place, and stores are well stocked this weekend," M&S told the BBC.

The retailer said on May 13 that certain personal customer data were stolen in a cyber attack, which could include names, dates of birth, phone numbers, home addresses, email addresses, home information and online order history.

It added that any card information employed is not available because it does not retain full card payment details on its system.

The hacker previously told the BBC's cooperative on April 30 that it had shut down part of its IT systems in response to the attack. The hacker has caused payment problems and widespread shortage of goods in stores, and data from customers and employees have been compromised.

It said Wednesday that customers should see stocks return to more normal levels on Saturday and Sunday.