Google will stop some Flash content from automatically playing starting Sept. 1, a move it decided on earlier this year to improve browser performance.
Flash, made by Adobe Systems, is still widely used for multimedia content, but security and performance issues have prompted calls to move away from it.
In June, Google said it planned to pause Flash content that wasn't central to a Web page but allow other content such as videos to autoplay. Flash, it said, can drain a user's laptop battery faster.
There are also security implications that Google didn't mention. Vulnerabilities in Flash are one of the most common ways that malware ends up on computers.
While Adobe in recent years has taken steps to improve Flash's security with speedier updates and code reviews, it still is a widely used attack vector.
The change will take effect from Sept. 1 for its Chrome browsers, Google said. Users will have the option to play the content, but they will need to adjust the browser's settings to automatically play content requiring a Flash plugin.
Google already converts Flash-based advertising content to HTML5, which allows certain types of videos to be played natively in Web browsers without additional software plugins.
The company encouraged those uploading ads to its Display Network to ensure that their ads can be converted to HTML5.