Secured Mode = Permanent War Protection (though you could turn it off if you desired)
On Fearless Blue, none of your countries will have Secured Mode. However, you can buy War Protection for 1 GC / country / 4 game months (1 rl day)).
On every other world, only your main country will be in Secured Mode. Every additional country will not be. Hoewever, again, you could purchase War Protection for 1GC / country / 4 game months (1 rl day in all worlds but LU where 4 game months is 16 hours).
By purchasing, I'm not sure if you're referring to buying one from another player on the Cash Market or buying a Computer Controlled Country for 100GC. If you're talking about buying a C3, I'd highly NOT recommend doing that. The cost is way too high. It's much cheaper for you to trade a few GC for Simcountry Dollars (SC), and buy some weapons and conquer the C3 instead. Even not knowing what you were doing (so you'd be quite inefficient at it), I can't believe it'd cost more than $2T MAX to conquer a C3, probably quite a bit less. That's less than 5GC.