Web-based malicious software, unlike other malware, is designed to implant itself on users' machines when they visit a certain Web site.

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"This additional level of protection when it comes to Safari users running Flash is good to see - as Adobe's software is so frequently exploited by malware authors and malicious hackers to infect web surfers, " said Graham Cluley, senior consultant at security firm Sophos in his blog.

BBC: Apple releases Flashback patch for older OS