every service I use to buy bitcoin
after submitting my credit card info
the process is declined because my card does not support 3D security
I don't understand what this means
but my card can buy anything online
The reason is most likely because merchants who accept credit cards for bitcoin is more likely to be victims of fraud than simple purchases of goods, because of the fact that bitcoin is irreversible as well as being extremely liquid which makes it perfect for a lot of the credit card scammers out there.
That's the primary reason that these exchanges ask for this 3D secure thing.
I honestly don't know what you can do in this case, other than contacting your bank and asking for a replacement card with this 3D secure thing, or even switching banks for that matter. However, you could try potentially linking the credit card to your paypal account, and purchasing BTC using Paypal on Virwox or other exchanges that way.
