Hello, I am wondering: is it possible that a virus or other infection can get onto my PC and remain undetected by my Avast anti-virus (free edition), and then be transferred onto my backup external hard drives when I am conducting a routine backup of files, and then destroy the data on my backup drives? In other words, can a PC infection "remain dormant" and unnoticed by PC security software, and then spring into action later, possibly on a backup drive? Or, am I safe to go ahead and back up my files to my external hard drives once i have done a scan that concludes my PC is currently "uninfected"? Thank you for clarifying!