Twitter has introduced a filter to stop users posting links to malicious websites, security firm F-Secure has revealed in a blog posting.
"Twitter hasn't announced this, but we just noticed that they have now started filtering Tweets that contain links to known malware sites," the blog posting said.
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Mikko Hypponen, chief research officer at F-Secure, said that as Twitter has been getting more and more popular, it is increasingly targeted by worms, spam and account hijacking.
"We've recommended Twitter to start filtering traffic to fight this. They can easily do it, as all the messages go through them," he said.
But some security experts claim Twitter's new filter does not block links to malicious sites that have been shortened.
In tests, Twitter blocked a link to a phishing site, but allowed the same link if it was shortened, according to reports.
Users of shortened links in Twitter will still have to rely on services like Bit.ly and Tinyurl to protect them from visiting malicious sites.