The theft has been ongoing since December 2015, according to the suit, which was filed on 8 August in a bid to find out the people behind the attack, according to a published report.
In the court filing, LinkedIn says it has the IP addresses of various attackers and is trying to use the case to make Internet providers give up their identities. In the absence of knowledge of the attackers' identities, the lawsuit cited "Does, 1 through 100" as defendants.
In June, Microsoft acquired LinkedIn for US$26.2 billion in cash. The deal is expected to close by the end of the year.
According to the lawsuit, LinkedIn has 400 million members in more than 200 countries and territories. Of this, about 128 million are in the US.
"To access this information on LinkedIn's site, the Doe Defendants circumvented several technical barriers employed by LinkedIn that prevent mass automated scraping, and have knowingly and intentionally violated various access and use restrictions in LinkedIn's User Agreement, which they agreed to abide by in registering LinkedIn member accounts," the filing said.
It claimed that the perpetrators had violated federal and state laws, including the Computer Fraud and Abuse Act and the Digital Millennium Copyright Act.
The company said it had drawn up spreadsheets and other reports tracking the ISPs, networks, and IP addresses used by the defendants, the dates and times of their activity and the number of pages they had accessed.
Also identified were fake member profiles said to have been created by the defendants, all of which were disabled after which additional technical safeguards were put in place to protect against unauthorised access.
The lawsuit said that LinkedIn had also collected information on the whitelisted cloud computing platform that the defendants manipulated to scrape data.
The firm said it expected it would be able to find out the identities of the defendants by serving third-party discovery on various ISPs and networks. "These entities are in possession of information that will help LinkedIn identify the Doe Defendants. LinkedIn intends to file a motion to expedite these discovery requests."