To make a mobile payment from NFC enable smartphone, the device should have special hardware called Secure Element. It stores details like account no, expiry date, etc in secure from.
The secure element stays isolated from the main memory, so limited predefined apps have access to it. So even if the hacker gets access to your smartphones. It's extremely difficult to pull out your financial details as it's encrypted in that secure element.
To make mobile payment using NFC, one needs an app like Google Wallet. An app like these has their own way of authentication. First, you need to unlock it using preset lock code and second to make a transaction over a certain limit (let say 80$), you have to enter a PIN, that was given to you while you install this app.
And the best part is a
contactless card or your smartphones don't store the PIN in them. So even if the hacker is somehow able to pull out your credit card details, he/she won't have the PIN to complete the bigger transaction. This makes sure that you are safe from a bigger loss.
Moreover, if someone can steal your smartphone/contactless cards, they can also steal cash from your pocket.
5. Smart Tags Can Be Made Read-Only
NFC security is not limited to mobile payment. Another popular use of NFC is in smart tags (or NFC tags). Which brings us to the question of
how secure are NFC tags?
By default NFC tags come rewritable. But you can make them read-only.  This ensure others can't tempered it.
For example, if you want your NFC tags to always open a link to your website, you can make it read-only. So that others can't change the information written on it. Useful when using NFC Tags in public.
Future of Mobile Payment?
This question reminds me of time when credit/debit cards was first introduced. People were skeptical about its use. People doubt its security and predicted that it won't work. And here we are now, using plastic card almost everyday. Same goes with NFC, people doubt its security but after seeing its benefits they will adopt this in future.
Conclusion
NFC is as secure as your credit and debit card. However, if someone wants to get something bad, they can go all the way to get it. The only thing that you can do is, make it harder for them. So until it's personal, they will leave you and move to some easy target.
Update your knowledge and increase the level of security, If you can do that, there is no need to worry when using mobile payment.