“Internet Explorer alert. Visiting this site may pose a security threat to your system!” is a misleading security alert that appears in Internet Explorer when you are infected with XP Guardian or Vista Guardian virus. This fake security alert claims that a particular website that you are about to open is dangerous and hosts harmful files. Then it will give you three options: install XP Guardian or Vista Guardian, scan your computer with anti-malware software or continue surfing without any security measures. Actually, no matter what you decide you will be prompted to buy the rogue security software. Don’t do that. This is nothing more but a scam. Instead, please read how to remove XP Guardian or how to get rid of Vista Guardian from your computer for free.