Twitter said Wednesday it has started tracking what other apps its users have installed on their mobile devices so it can target content and ads to them better. "To help build a more personal Twitter experience for you, we are collecting and occasionally updating the list of apps installed on your mobile device so we can deliver tailored content that you might be interested in," Twitter said.

Twitter users will receive a notification when the setting is turned on and can opt out using settings on their Android or iOS phones.

Twitter clarified that it is only collecting the list of applications users have installed and not any data within the applications.

Besides advertising, Twitter said knowing what apps people have downloaded can improve its suggestions on what accounts to follow and add relevant content to their feeds that isn't advertising.

Twitter has also introduced Twitter Offers, which enable advertisers to create card-linked promotions and share them directly with Twitter users.

When users see a Twitter Offer in their timeline, they can add the offer to their credit or debit card in just a few taps, and redeem in real time by using the card at the store. After the purchase, the cash back savings appear on their card statement within a few days.

With Twitter Offers, advertisers will be able to attribute redemptions directly to their campaigns on Twitter, so that they can effectively measure the ROI from their promotions, even when redemption happens offline.

Twitter is planning to work some brands to begin testing this new feature during the holidays in the U.S.