Twitter has added Charlie Miller to its security team. Friday marked the last day that the well-known vulnerability research expert held his post at security firm Accuvant, as he will soon be taking the title of software engineer at the popular social network based in San Francisco. The white hat hacker announced his career move in a tweet Friday. It remains unknown what Miller will be working on at Twitter, but there is a likelihood that the company could use his penetration testing skills to scan its service for vulnerabilities. At this year's Black Hat conference in Las Vegas, Miller discovered a weakness in near field communication that could have end-users' smartphones compromised through physical contact.