Twitter opens door for advertising

Some analysts are sceptical that advertising will catch on in a meaningful way on social networks, arguing that companies are reluctant to juxtapose their brands with unpredictable, and potentially offensive, user-generated content.

Stone himself has said the company was wary of annoying its growing base of users by pummeling them with ads.

But other analysts point out that users of social networking websites tend to spend a lot of time on those sites, providing an attractive platform for advertisers to promote their brands -- especially if preferences are tracked.

Twitter kept its new clause on advertising open-ended, and stressed it was subject to change.

"The services may include advertisements, which may be targeted to the content or information on the services, queries made through the services, or other information," the terms read. "The types and extent of advertising by Twitter on the services are subject to change."

"In consideration for Twitter granting you access to and use of the services, you agree that Twitter and its third-party providers and partners may place such advertising on the services...."