From this point on, beware of who you follow on Twitter. Shiva Rajaraman, Twitter’s product manager, announced at a London ad conference that the wildly popular microblogging service is building an “interest graph” that will allow advertisers to target users more effectively via its advertising platform, Promoted Tweets. Using this graph, brands will be able to tailor their advertising efforts based on who users are following and what type of information they’re looking for. For example, a baby food manufacturer could promote its tweets to parents who follow TwitterMoms networks.

Said Rajaraman at the conference: “Moving forward, [with promoted products] we are looking at introducing a targeting mechanism [which is based on an interest graph] … We can build out a person’s interests based on who they are following…We are experimenting with how we can assemble those pieces of information together and show people’s interests.”

Privacy hawks can rest assured, added Rajaraman, that people’s interests would not be attached to their name, but rather broad categories such as ‘computers’ will be grouped together for the benefit of advertisers.

With people posting 90 million tweets a day, it’s no wonder Twitter is capitalizing on its growing prowess as an advertising vehicle. In fact, according to the results of a recent survey, 65 percent of Fortune Global 100 companies are now tweeting away. That’s more than are on Facebook, YouTube or in the blogosphere.

Twitter launched Promoted Tweets back in April, enabling companies for the first time to pay to have their posts top search results. The program rolled out with a handful of advertising partners including Best Buy, Bravo, Red Bull, Sony Pictures, Starbucks, and Virgin America. According to Twitter’s guidelines, Promoted Tweets are clearly labeled as “promoted" when an advertiser is paying, but in every other respect they first exist as regular Tweets and are organically sent to the timelines of those who follow a brand. Promoted Tweets also retain all the functionality of a regular Tweet including replying, Retweeting, and favoriting. Only one Promoted Tweet is displayed on the search results page.