Link shortners are now used extensively on web. They are good for websites with character limit, like Twitter. They are even useful outside twitter. But spammers and hackers are using this useful tool to trap novice users on social networking sites.
As I have seen, TinyURL is the most used link shortner by spammers and hackers. There is a strong reason for this! Have you ever noticed that, link shortend using TinyURL don't expand to original site on hovering your mouse cursor on it, but most of the other services do ?!
Yes, TinyURLs won't expand to original site on hovering mouse cursor, which helps hackers to hide the evil URLs from users ! Without knowledge, if you click on those links, you are inviting danger! After getting infamous for this cause, TinyURL has now taken steps to avoid this.
Now you can preview URL (or let us call it Web Address) of original site before going to that site. All you have to do is, go to tinyurl.com, click on 'preview feature' [found on left sidebar of the homepage] and click on 'click here to enable previews'. That's it, now, everytime when you click on a TinyURL link, you will be taken to TinyURL website and original link will be revealed. First of all, your browser cookies must be enabled.
Even though this doesn't secure your twitter account completely, it allows you to decide whether to go to the original website or not, thus reducing possible traps :)