The social media company will collect information about people when they visit third-party websites, but people's data won't be collected when users are logged-out of Twitter.
This follows Twitter's announcement on Thursday of an experiment to offer people 'tailored suggestions' about who to follow. Twitter will use widget data to track new users so it can do this, according to the updated policy.
"We may tailor content for you based on your visits to third-party websites that integrate Twitter buttons or widgets," said Twitter. "When these websites first load our buttons or widgets for display, we receive log data, including the web page you visited and a cookie that identifies your browser."
Exisiting Twitter users' data is monitored in line with the social network's previous privacy guidelines. However, log data will now be sent to the company every time any user visits a third-party website via a Twitter button.
"Log data may include information such as your IP address, browser type, operating system, the referring web page, pages visited, location, your mobile carrier, device and application IDs, search terms, and cookie information," Twitter said.
Log data will be kept for 18 months. After this it will either be deleted or details such as username, full IP address and email address will be removed. Widget data will begin to be deleted after a maximum of 10 days.
Twitter will use widget data in a similar way to companies such as Facebook, Othman Laraki, Twitter's director of growth and international, said in a blog post.
"We receive visit information when sites have integrated Twitter buttons or widgets, similar to what many other web companies — including LinkedIn, Facebook and YouTube — do when they're integrated into websites," said Laraki. "By recognizing which accounts are frequently followed by people who visit popular sites, we can recommend those accounts to others who have visited those sites within the last 10 days."
Facebook has been under investigation by a number of privacy authorities, including the Irish Data Protection Commissioner, over its use of tracking technologies.
People who don't want to receive tailored suggestions can log out of Twitter or turn on Do Not Track browser settings, according to Twitter's help center.
The social media company supports Do Not track by removing the cookie that links a new user's browser to visits to websites, it said.