NHK has learned that hackers have stolen classified data from major Japanese auto parts maker Denso and are demanding a ransom.

Information security firm Mitsui Bussan Secure Directions says a group called Pandora posted a message on the dark web on Sunday afternoon, Japan time, saying that it had stolen more than 157,000 items.

The group says the 1.4 terabytes of data belonging to the Toyota Motor group firm includes purchase orders, emails and drawings.

Pandora is believed to carry out cyber-attacks to encrypt data and demand money in return for decryption. It also threatens to release data if the demand is not met.

Denso told NHK that it had confirmed unauthorized access to the network of its business base in Germany and is looking into whether the access would affect operations.

Toyota had to suspend operations at all its plants in Japan last month after one of its suppliers was hit by a cyber-attack.