So if I hack your details from a company you've bought something from and use that to access and drain your account, your anti-fraud measures prevent this?
No, but you're not liable for that, the company and your bank are. You'll have some hassle getting it back, but the bank want hold you liable for all your money being nicked, because then no-one would bank with them. They want people to use cards and spend money online, because as you have stated, they make more money that way, so it's in their interests to ensure you are secure.