1. Internet today is all but a minefield of boogies,traps and malware.....every day so many threats are born....though most of them die but still a huge percent of them survive the security walls and become stronger by time as they are able to remain live and acvtive.In recent times shortened URLs have become popular amongst users (including me...:-) to conserve the typing space like in microblogging sites viz twitter etc.So typically a naive(???),prone user who submits his long URL to a site to get a shortened URL receives a second,specially coded shortened URL that redirects to the original URL.So here lies the weak hole that is most of the times exploitable by the attacker...because the actual destination URL is hidden in it....so going by the looks...there is nothing to worry...but it is the redirection that is a cause of worry...it may be right or may be redirecting to a malicious link....!!!!so when some one uses a free URL shortener ,he does not have control over that shortened link. And, should something happen to the provider of that URL shortener, then he risks redirecting ALL of shortened links elsewhere!!!
2. We all know that clicking links is pretty tempting....so it is just a matter of one redirected malicious link click that makes the difference....so whats the solution????...actually companies like Facebook,Gmail, SBI, Paypal ,twitter etc are offering users the option of persistent SSL encryption and authentication across all the pages of their services including the login and all accessible pages.....but this does not stand good for all...for these sites also..it is optional to vide the settings for accessing....