ebay account security, authentication app?

[bashort]

I had thought that two factor authentication was basically a foolproof way to secure a account, I thought this right up until I had another account with two factor  somehow hacked and unauthorized purchases were made.

I read about authentication apps but do not really understand them and am worried that this app is just another door for hackers to enter through.

Anyone have any advise? 

[lakefor94]

All I can offer up is that I keep my passwords at ~12-15 characters and mix them up with numbers, special characters, include upper case etc.

Never been hacked in anyway, ever.

Do I need two factor?