I don't know if this sentence is 'wrong,' per se, but wouldn't it be weten instead of kennen, since a password is more like a fact to memorize than a concept to be familiar with?
Ik gebruik computers, dus ik ken over wachtwoorden--I use computers, so I know about (i.e., am familiar with) passwords. But Het kind weet de wachtwoord van zijn ouders, en gebruikt hun computer zonder hun permissie--the child knows (i.e., has memorized and now uses) his parents' password, and uses their computer without their permission.
A quick Google search reveals that no one ever says ik ken over dit ding, so it seems you have to use a noun phrase, for example ik weet de facts over dit ding.
Ast for using weten with noun phrases, it's apparently sometimes correct and various forms of een wachtwoord weten seem to give a lot of hits on Google.