A self-propagating worm, named yhoo32.explr, installs a piece of software called ‘Safety Browser’ and then hijacks the Internet Explorer homepage, leading users to a site that puts spyware on their PCs.
Because Safety Browser uses the Internet Explorer icon to identify itself, users can easily mistake it for the legitimate Microsoft browser.
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Sneaky, but I cant find any information on Firefox and since I dont personally use Yahoo messenger it doesnt really affect me.