LinkedIn has confirmed that member information is being offered for sale online.
wrote earlier this week that it concerns information from 500 million people.
The news follows days after data from 533 million Facebook users went online.
According to the anonymous seller, this concerns data such as usernames, e-mail addresses and telephone numbers.
Of the 500 million data contained in the package, 2 million have been released as an example.
LinkedIn says it has viewed the data and concludes that it is not just about LinkedIn data.
"We examined the set of alleged LinkedIn data and concluded that the information comes from various websites and companies," the company writes.
It is not known which other sites and companies these are.
The data from LinkedIn profiles is, according to the company, information that was publicly available.
"That public information appears to have been copied from LinkedIn. But this is not a data breach and, based on what we found, no private information has been leaked."
According to the company, copying and saving of the data (also known as scraping) is prohibited.
"If people try to copy data from our members and do something with it that is not approved by LinkedIn or our users, we hold them accountable."
It is not clear whether LinkedIn will warn users that their data may be for sale.
Facebook previously said it would not and advised users to check their privacy settings.
In Italy, the regulator has started an investigation into LinkedIn,
See also: What to do if you are a victim of a major data breach