The twitter terms follow much of the same template for social networking sites. While they specifically ensure that content you submit through their service is owned solely by you, they do reserve the right to collect and use information you display for their own royalty free purposes. Basically, you own your content and and they can’t claim anything you post as their own intellectual property. However, you agree to allow them and third party partners to use information free of charge as they evolve their services.
In the event of security breach, the terms absolve twitter of any responsibility of any damages incurred through the use of their services and any liabilities they might be stuck with will not exceed 100$ USD. The reason for this inoculation against damages is that it allows for an open platform environment. The exceptions would be if the malicious party is from the company itself.