A virtual machine is basically a small PC which you have inside your PC. An example of a virtual machine is VMware. That's a paid one, which you pay, and install on your machine. Even though it looks safe to run malware on it, etc, some malwares are designed and developed very well to break through and reach your real PC and harm it. So, it's not 100% safe, and you should know what you're doing if you're testing malware and anti-malware applications. I do these testing myself, and no malware has managed to harm my real PC yet, and I've been doing this for several years. But I know there are some malware which is built for doing these kinds of things, so be aware.

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