Taiwanese researcher Orange Tsai thought he had stumbled on some malicious activity in Facebook’s network. But, according to a statement from Facebook on Friday, what he found was something else. Tsai used the vulnerabilities to gain access to Facebook’s corporate server and gather information from its logs. He spotted some unusual errors in the server’s log that pointed him to what turned out to be a PHP-based backdoor. Facebook had a different explanation for what Tsai discovered on its servers; it said the “hackers” Tsai had detected was actually another researcher.”]