Recently, Twitter implemented technology to help stem the threat of malicious URLs being propagated though its service. This approach seems to be a great effort on the part of Twitter to prevent attackers from tweeting malicious links. It appears as if the tool is filtering tweets and comparing any embedded URL to their list of known malicious sites. Trying to determine whether a URL points to a malicious website in a large-scale automated fashion, especially in today’s threat landscape, is a challenging problem. From my perspective, there are a few issues that need to be worked out. Twitter is likely in the nascent stages of addressing these types of issues and we expect they will try to overcome the associated limitations. To date we've only seen a relatively small number of attack attempts involving malicious URLs on Twitter. URL-shortening services are often at the heart of these types of attacks as bad guys try to take advantage of the system to disguise malicious links and sneak them past anti-phishing and anti-spam filters. So, although shortened URLs do carry certain advantages they also introduce new threat possibilities that attackers have been exploiting. My colleague, Zahid Raza, posted an excellent write-up titled TinyURL—The Tiny Fear, which discusses the threat possibilities associated with shortened URLs. Overall, it’s great that Twitter is taking steps to curtail this issue before it becomes a bigger problem. Their proactive stance demonstrates that the online social networking industry continues to move in the right direction towards further protecting users.