Sobrier gathered 1,587,824 tweets from the Twitter public timeline and found that Bit.ly accounted for 33% of all URLS, as opposed to 5% for TwitPic, which occupied the number two spot. Take a look at the breakdown below:
Sobrier performed a similar analysis last March, analyzing more than 1 million tweets. Since then, Bit.ly has actually lost some ground, as have several others. Noticeably absent from the list of URL shorteners is t.co, Twitter's own URL shortener. Perhaps this has fallen into the "Other" category for now. According to Sobrier, Google represents 5% of all URLs, while social services like Foursquare and Facebook have also been gaining ground.
As part of his analysis, Sobrier also looked at malicious shortened links, finding that just 0.07% of all links were considered "dangerous".
The majority of malicious links were served up on Bit.ly, with a high percentage on TwitThis, which Sobrier attributes to "hijacked WordPress installations serving malware".