A federal judge has ruled that Google won't have to face a class-action lawsuit for allegedly violating email users' privacy by scanning their messages in order to place ads around them. The lawsuit alleges that Google violated the federal wiretap law by intercepting emails without permission.

U.S. District Court Judge Lucy Koh's ruling means that consumers that want to sue over the practice must do so as individuals and not as a group. Legal sources, however, said individual suits are prohibitively expensive.

Koh said a class-action wasn't appropriate because one of the key questions in the case centers on whether users consented to Google's practice of scanning messages. Koh said that determining consent required "an intensely individualized" evaluation of the facts.

"A fact-finder would have to determine to what disclosures each class member was exposed and whether such disclosures were sufficient to conclude ... that class members consented to the alleged Google interceptions of email," Koh wrote.

"The individualized questions with respect to consent, which will likely be Google's principal affirmative defense, are likely to overwhelm any common issues."

Koh rejected Google's argument to dismiss the case last September. She rejected Google's argument that all Gmail users consented to the scans.

She ruled that Google's terms of service weren't clear enough to notify users about the company's practices. Koh also rejected Google's argument that all non-Gmail users "implicitly" consent to the scans.

Koh said some email users could have consented to the scans regardless of Google's terms of service. For instance, she writes, people who used Gmail after reading about its practices in the newspaper might have implicitly consented to the scans.