Popular micro-blogging service Twitter has announced that it has made changes to its Terms of Service.

The changes are designed to "leave the door open for advertising" and clarify content ownership as well as address the increasing problem of spam on the service.

"Now that we know more about how Twitter is being used, we've made changes to our Terms of Service ... The revisions more appropriately reflect the nature of Twitter and convey key issues such as ownership", says Twitter boss Biz Stone in a blog post.

"Your tweets belong to you, not to Twitter", assures Stone, althought the terms allow Twitter to "use, copy, reproduce, process, adapt, modify, publish, transmit, display and distribute" your tweets.

Other tweaks relate to APIs, spam and abusive behavior. Stone ends his blog post with, "It's important that everyone who tweets, develops apps, or is simply interested in Twitter understands that it's not about the technology, it's about how we all use the service that matters most".