They were shared on the Internet via Raidforum, which is notorious for selling stolen data, by an account holder named ‘kjkwwfw’ last Friday.

The full profiles were not uploaded, but full access has been offered for those willing to pay a negotiated price.

The profiles would be updated monthly, the account holder said.

VnExpress verified through the phone numbers that the personal information offered is accurate.

Most victims are not aware that their Facebook accounts, included in the leak, were being sold. A common factor among the hacked accounts was frequent Facebook use for online shopping.

Dinh Long, a Hue-based cybersecurity expert, said the data might have been stolen from multiple online shopping sites.

"These are the data of online shoppers."

He said it is possible the hackers do not have all 300,000 profiles as they claim, and only do so to seek "attention."

Vo Do Thang, director of cybersecurity firm Athena, said the leaked data could expose people to spam and unwanted adverts, and even phishing calls.

Their physical addresses might also be used to make fake deliveries, he warned.

The responsibility for this incident would fall on the firms and businesses who have their customers’ data, he said.

This is not the first time Vietnamese personal data has been offered on sale on Raidforum.

Late last year around a million Facebook users’ data was leaked on the forum with account names, locations and email addresses.