The bonsai Mastercard is not insured against fraud. Insurance means that you pay a (monthly) amount to cover you against fraud and that we immediately reimburse you (part of) the amount. Because the bonsai Mastercard is completely free, there is no insurance. It is possible to try to dispute a specific fraudulent transaction via Mastercard. This is called a "Chargeback" and is only possible if certain conditions are met. This means that Mastercard is a safer option for online payments than, for example, a bank transfer!
Do you think you have been a victim of fraud? Then read here what the next steps are.