Purveyors of spam and malicious software are taking full advantage of URL-shortening services like bit.ly and TinyURL in a bid to trick unwary users into clicking on links to dodgy and dangerous Web sites. Fortunately, with the help of a couple of tools and some common sense, most Internet users can avoid these scams altogether. According to alerts from anti-virus vendors McAfee, Symantec and Trend Micro, the latest to abuse these services is the Koobface worm, which targets users of social networking sites like Facebook (Koobface is an anagram of Facebook) and Myspace. It’s now also spreading via microblogging service Twitter. Koobface arrives as a message that urges users to click on a link to a video, which invariably leads to a site that prompts the visitor to install a missing video plug-in. The fake plug-in turns the user’s system into a bot that can be used for a variety