Twitter, the fast-growing micro-blogging site, on Thursday took a first step toward making money by revising its terms of services to allow advertising.

“We leave the door open for advertising. We'd like to keep our options open, as we’ve said before,” Biz Stone, Twitter’s co-founder, wrote on the company’s official blog.

The ads will be targeted at the information on the service, according to the company.

To avoid a Facebook-like controversy–Facebook earlier this year claimed ownership of its users' info and then quickly reversed that decision–Twitter also offered more clarity as to who owns the "tweets," or messages posted.

The startup wrote on its blog Thursday that it “is allowed to use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute your tweets because that's what we do. However, they are your tweets and they belong to you.”

The San Francisco company, which lets users share their thoughts online in posts that are up to 140 characters, claimed more than 50 million visitors in July,  or 15 times more users than during the same period last year, according to market researcher comScore.