What Antiviruses look for is a program that can take advantage of your computer's inner workings. Trojan Horses for example, like njRAT work by connecting your computer to a static DNS controlled by the hacker through a simple client/server setup.
Is it also worth mentioning that njRAT was coded in Visual Basic .NET?
https://www.youtube.com/watch?v=mZBeLFKvUis
Here's a Trojan Horse in action, from the hacker's side for instance.
What you're forgetting is that files can always be recovered. In fact, all Windows PCs with the Windows 2000 operating system and newer have this feature. Really the only way they couldn't be recovered is if you were somehow dumb enough to infect yourself with WannaCry.
My point is just that an online antivirus scan is only meaningful when it finds a virus.
I understand that and I apologize if I've jumped the gun on you.
The difference between simply deleting a file, and encrypting it is that the file becomes unusable after the fact, and a smart programmer would learn how to circumvent ways to recover those files by usual means, for instance, deleting every System Restore point.
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Was your RAT a direct-connection rat, to where you must connect to the user's computer by typing in his LAN address (assuming you're testing using VMs) like old trojan horses in the 90s (Netbus, Sub7, etc) or was it a reverse connection rat, like the ones that have become conventional today to where your computer acts as the server, and each victim's computer becomes a client connecting to a DNS that you set up? Or as you said, something with no malicious intent like a Teamviewer clone?
That's ok, and I also apologize if I've been overly critical of you. :)
I wasn't aware that System Restore includes documents. Isn't the purpose to restore the system to a functioning state if the registry or software gets messed up? As far as I know, it intentionally avoids the Documents folder. Out of the box, I don't think Windows keeps any kind of secure backups of personal files. (Possibly OneDrive, but I think that still requires setup.)
That's a neat video of njRAT in action! It looks remarkably similar to mine (which I wrote before I even knew what a RAT was). In my RAT, I hardcoded my computer's IPv6 address. When the program loads, it reports the destination IP address to me, which I keep in a list. It then maintains an idle HTTP connection, waiting for instructions. I wrote a master control program that lets me "open" any online computers. I can transfer files, use the clipboard, and remotely control the mouse and keyboard while viewing the screen. It's not meant for collaboration, but rather to provide centralized access. I have a bunch of computers around the house, so this is quite a time saver.