Tesco-owned Asian supermarket Homeplus is under investigation in South Korea after prosecutors accused the group's managers for selling customers' private information to insurance companies.
South Korean authorities are also probing Homeplus for rigging a customer competition following allegations that employees rigged the results so friends would snap up the main prize of a BMW.
Tesco serves over six million customers in South Korea every week across 400 stores and 198 franchise shops.
Tesco said in a statement: "We can confirm our South Korean business, Homeplus, is under investigation regarding the handling of customer data.
"We take the protection of our customers' data extremely seriously and are co-operating with the investigation."
Another Problem for Tesco
Tesco revealed that it overstated its profits by £250m (€318m, $409m) and has since drafted in the former chief financial officer Alan Stewart, two months ahead of schedule.
Tesco had already cut its full-year profit forecast from £2.8bn to £2.4bn in August.
It has also since suspended four executives, including UK managing director, Chris Bush, while media reports have speculated that the others include food commercial director John Scouler and the head of food sourcing, Matt Simister.
Tesco has also launched an internal investigation, led by Big Four accountancy Deloitte.