Like smallpox, terrorism is something Libertopians never worry about. Most people have probably forgotten either problem once existed. Both are diseases which were eliminated when the causes were eradicated. States caused terrorism just as surely as viruses caused smallpox.
Sure, there are sometimes violent attacks here or there. What difference does it make why the attacker does what he does? The results, and consequences, are the same. However, now there is no State whipping up violent extremism and hunger for revenge. So, even without Homeland Security [sic], the attacks are very, very rare- almost nonexistent.
Of course, without a State to make enemies around the globe, and to influence politically, it isn't worth the effort to attack random innocent people. Libertopians are pretty much universally armed. You'll die and no one will fear "your cause".
I admit it is hard for me to even hard for me to think about what terrorism might have been or how it might have been thought about. How unsettling it must have been to watch a State continuing to take actions which put your loved-ones at risk, while it simultaneously violated your liberty, using the terrorism its own actions caused as justification. It's no wonder some people .... Ah, I almost fell into the trap of revealing too much about your future. Don't worry. You'll soon see what I was referring to.