[a9t9]

Extension can/could read all data that you enter in websites. So you should only install extensions from trusted sources/developers.

And/or: What I do is to have one Chrome profile for important websites (e. g. online banking) and another one for the casual web surfing. This "casual" profile is where I try out all new extensions. And only the ones I really need are used in the "secure" profile as well.