Because Windows Vista reached its end of life years ago, it no longer receives security updates from Microsoft. If you are using a full version via a VM, (like banking) and be cautious when connecting it to the internet, as it is highly vulnerable to modern exploits.
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If you still want a VM, use (free) and install Vista SP2. Do not connect it to the internet – Microsoft stopped updates, and it is a security risk. Because Windows Vista reached its end of life