If your wallet.dat file is stolen, and it's unencrypted & you have no backup of the file, it's the equivalent of cash being stolen; there's no way of getting it back unless you catch the thief. Thusly, you must take proper precautions to prevent the loss/theft of your Gridcoin.
One of the most common attack vectors is through your web browser, so take precautionary measures to minimize risk of loss of funds/exposure to malware.
It's crucial that your private communications online are not intercepted by any malicious entity; privacy is a human right, take yours back!
Most of these tips are a given, but it's good to remember that they are quite important to adhere to at all times.