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C:Drive getting killed
they would have to find some means to rooting your machine, such as finding some open port you may have from malware or whatwhatnot, sending you some infected file with a rootkit, etc. the important part is that they need admin rights to get the drive formatted. or if you are running as admin and they send you a bat file (or any file for that matter thats infected) it will execute with your privileges and then you're phucked