Twitter is one of the famous social sites and thus it has become one of the prime targets of the hackers as well as it becomes easier to infect large number of people from here. The latest form of the attack that is being spread from this is the link redirecting to some malicious site.
Many users posts some links on the twitter website in the form of tiny urls like the one from google url shortening service called goo.gl but hackers have deployed this technique to spam users’ wall with short links which on clicking redirects to malicious websites.
What these websites does is, they will ask you to install some antivirus from their website to be safe from the virus etc. but in reality it will be more of a fraud tool rather than an antivirus. Thus it is advised for all the internet users to be safe and do not open just any site on the net.
Also to protect from short URLs what you can do is use url unshorten sites like Untiny.