Hacker be mitigated. White hats are usually employed by the target system's owner and are typically paid (sometimes quite well) for their work. Their work is not illegal because it is done with the system owner's consent. Black hats or crackers are hackers with malicious intentions. They often steal, exploit, and sell data, and are usually motivated by personal gain. Their work is usually illegal. A cracker is like a black hat hacker, but is specifically someone who is very skilled and tries via hacking to make profits or to benefit, not just to vandalize. Crackers find exploits for system vulnerabilities
Severin Hacker that that it would be accessible for non-English speakers. They felt that automated translation software wasn't as effective as using the skills and knowledge of bilingual speakers. During Hacker's doctoral studies, Duolingo became a by-product of this idea, or "happy mistake." Hacker's goal for Duolingo was to make it "100% free" so the most disadvantaged person with an internet connection would still have access to it. Hacker and his team of PhD students used machine learning to personalize Duolingo to each user. Specifically, they wanted to predict what language concepts the user was on the verge of forgetting. In 2012,