A U.S. appeals court said Google must face a revived lawsuit by Google Chrome users who said the company collected their personal information without permission, after they chose not to synchronise their browsers with their Google accounts.

The 9th U.S. Circuit Court of Appeals in San Francisco said the lower court judge who dismissed the proposed class action should have assessed whether reasonable Chrome users consented to letting Google collect their data when they browsed online.

Tuesday's 3-0 decision followed Google's agreement last year to destroy billions of records to settle a lawsuit claiming the Alphabet unit tracked people who thought they were browsing privately, including in Chrome's "Incognito" mode.

Google said in a statement: "We disagree with this ruling and are confident the facts of the case are on our side. Chrome Sync helps people use Chrome seamlessly across their different devices and has clear privacy controls."

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Matthew Wessler, a lawyer for the plaintiffs, said he was pleased with Tuesday's decision and looked forward to a trial.

The proposed class covers Chrome users since July 27, 2016 who did not sync their browsers with their Google accounts.

They said Google should have honored Chrome's privacy notice, which said users "don't need to provide any personal information to use Chrome" and Google would not receive such information unless they turned on the "sync" function.

The lower court judge concluded that Google's general privacy policy allowing data collection applied to the case, because the Mountain View, California-based company would have collected the plaintiffs' information regardless of which browsers they used.

In Tuesday's decision, Circuit Judge Milan Smith called that focus misplaced.

"Here, Google had a general privacy disclosure yet promoted Chrome by suggesting that certain information would not be sent to Google unless a user turned on sync," Smith wrote. "A reasonable user would not necessarily understand that they were consenting to the data collection at issue."

The appeals court returned the case to U.S. District Judge Yvonne Gonzalez Rogers in Oakland, California, who had dismissed it in December 2022.

Google's settlement related to Incognito let users sue the company individually for damages. Tens of thousands of users in California alone have since done so in that state's courts.

The case is Calhoun et al v Google LLC, 9th U.S. Circuit Court of Appeals, No. 22-16993.