Twitter has modified the terms of service that govern the proper user of the microblogging and social-networking site to state unequivocally that messages posted belong to their authors and not to the company.

"Twitter 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," wrote Twitter co-founder Biz Stone in a blog post Thursday announcing the modifications.

There has been controversy over the question of who owns the messages, photos, videos and other material that people post to social media and social-networking sites like Twitter, Facebook, MySpace and YouTube.

For example, Google and Facebook got into hot water when critics complained about what they perceived as terms of service that claimed ownership of the data end users store in Google Apps and Facebook profiles.

The revised Twitter terms also state that end users allow Twitter to make posted messages available to external applications that use the Twitter API (application programming interface).

However, Twitter is still hammering out a set of guidelines for developers on the proper use of the API.

The API guidelines are still in draft form and require that developers identify the authors of "tweets," maintain the integrity of the text and obtain permission to send messages on end users' behalf or turn their message into a commercial product, like a poster.

Twitter is also keeping mum on details about the display of advertising on the site, an issue of much discussion among pundits who follow the company and have raised questions about how it will generate advertising to sustain its business.

Twitter welcomes feedback on its terms of service and will revise them as it deems necessary.

"These updates complement the spirit of Twitter. If we've left something out, or the nature of the service changes, then we'll revisit the Terms -- there's a feedback link on the page," Stone wrote.