The exposure of thousands of phone numbers, which Motherboard obtained from a source, has not been previously reported.
The online trading company said a hacker obtained email addresses of 5 million users, and full names of 2 million users.
The plaintiffs hope to turn their lawsuits into class actions potentially representing millions of people against Syniverse.
Some people believe the hourslong outage may be linked to a supposed data breach that is, most likely, actually a scam.
Syniverse handles billions of text messages a year, and hackers had unauthorized access to its system for years.
Hackers selling the data are claiming it affects 100 million users.
Hackers claim they found the data of millions of Audi customers on an unsecured server hosted on Microsoft Azure's cloud.
Analysis by Motherboard and a security researcher indicate the database is separate from the recently reported cache of 500 million accounts.
The data from companies such as Google, Twitter, AT&T, and Verizon can include GPS coordinates and browsing history.
A database containing the stolen phone numbers of more than half a billion Facebook users is being freely traded online.
Unknown attackers tried to compromise the source code of the PHP programming language in what would have been a dangerous supply chain hack.
A data breach that already hit bank employees just got much worse