The Islamic State in Iraq and Syria (ISIS) uses a 34-page manual to instruct its followers on how to stay invisible on the Internet. The Arabic document was translated and released this week by analysts at the Combating Terrorism Center, an independent research group at the U.S. Military Academy at West Point. It includes warnings to avoid Instagram because it is owned by Facebook, and Dropbox because former secretary of State Condoleezza Rice sits on its board of investors. Famous government leaker Edward Snowden has also criticized Dropbox over its privacy, the document notes. Users are also directed to use...