Uber recently landed in trouble because 57 million of its users had been hacked, and the company spent a bunch of money to deliberately hide that fact from the rest of the world.
According to Uber, the 2.7 million figure is "approximate rather than an accurate and definitive account" - this is because the information gathered by the firm's app does not always specify where users live.
The lawsuit alleges that Uber experienced a smaller data breach in 2014 and, although the company vowed to update its security practices in order to meet industry standards, it failed to do so, leading to the 2016 breach, NBC Chicago noted.
The October 2016 data breach of Uber's systems affected up to 2.7 million user accounts in the United Kingdom belonging to both customers and drivers, it has emerged.
Ferguson's lawsuit is the first from a state, although attorneys general in New York, Missouri, Massachusetts, Connecticut and IL have begun investigations, and the city of Chicago and Cook County have filed a lawsuit.
In a statement released today, the UK Information Commissioner's Office (ICO) says that the breach may involved 2.7 million UK user accounts. "Consumers expect and deserve protection from disclosure of their personal information".
The firm has said it has a total of five million active users and 50,000 drivers in the UK.
"Washington law is clear: When a data breach puts people at risk, businesses must inform them", Ferguson said in a statement on Tuesday.
The Data Privacy Act penalizes the concealment of security breaches involving sensitive information with imprisonment ranging from 18 months to five years and a fine of not less than PHP500,000. NY fined the company US$20,000 a year ago over a 2014 data breach. The ride-hire company denied that other, more sensitive information like user financial details or location history had been compromised.
"We are monitoring the affected accounts and have flagged them for additional fraud protection", the company said.
Uber also faces lawsuits filed by consumers over the issue.