Twitter shortens the URLs with its own link shortening service. The Safe Twiit online service from F-Secure will tell you whether the last 30 links are safe or not.
This service will scan the last 30 tweets from your timeline, profile and mentions.
You will have to authenticate this service to access twitter first.
The access permissions are
Scan your Twitter for malicious links - http://safetwiit.f-secure.com/ (This service is in beta stage.)