A botnet is a PC connected online that is used to do a task, so practically any PC can be used for this purpose even without the owner knowing. It can be hijacked to covertly perform a task from the attacker on the background and still function as it normally would, hence lowering the possibility of discovery. Aside from those, Hass and Associates Cyber Security also found out that botnets could replicate automatically to other legit viewers by links in the chat of a stream, for instance. The malware could also make itself look like an update from Google or Adobe to infect a PC.
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