Andy Coulson, the prime minister's former press secretary, was arrested Friday in connection with allegations of phone hacking and corruption in a case that promises to be a growing political liability for David Cameron. The scandal has prompted questions over the prime minister's judgment in hiring Coulson after he resigned as editor of the News of the World because of the allegations. Speaking shortly before his former aide's arrest was announced, Cameron went on the defensive at a Downing Street news conference Friday, saying: "The decision to hire him was mine, and mine alone." He said he gave Coulson a second chance after assurances that he was not involved in wrongdoing at the newspaper.