I just unlocked FOBs.
How do I stay safe GAF? I've heard of people going to bed, coming back and their shit is messed up.
It's all up to your luck. I've had my FOB standing for two weeks, and haven't had a single invader.
It's possible that was because I opened it with a security team level 28 and immediately developed all possible security devices, and built several struts (which apparently raise the defense level of the platforms).
And since I haven't invaded anyone, I don't have any PF points, which leaves me in the same place as people who just got their own FOB's (and that's generally those that don't have any defenses or are bad players), which probably explains why I haven't been invaded.
Other explanation is Konami's servers suck.
EDIT: It's not explicitly said, but developing mines and decoys actually improve the security of the FOB. Take that in account. One slightly hidden mine that is activated by a careless invader can be the key point of preventing their success.
I went nuclear and wiped out a guy's base after he stole a few fuel containers from me. Basically, if your FOB get's punched in the gut, you punch back harder.
And this. Make people fear you.