Can internet searches cost you your clearance?

Big Brother is always watching and listening, and they have many tools. Sniffer programs key on searches, phrases and keywords. Unless he triggers monitoring and is not breaking the law he probably has nothing to worry about. If he googles "Build a Nuke" it might spark interest. If he starts trying to acquire these items and leaves a paper trail with credit cards, he may have an issue. Most of those guys use Dark Web, but Feds are on there also. Don't break the law or show intent to and you'll be fine.

Not likely, unless he is doing his googling from a government computer. Actually, most of the really cool stuff is blocked on the .mil. As a cyber instructor, there are things I have to research which can't be done from the .mil so I have to do them from home.

Depends on the subject matter. A civilian can lose a job because of the internet such as face book history and so can a Soldier get himself in trouble. Researching how to make weapons also depend on what you want to make. Bombs are considered weapons of mass destruction. I believe there is monitoring of selected site such as that and other types of weapon modifications. A good example is converting weapons to fully automatic fire. The internet is a dangerious research facility to stupid people.