A May text message conversation with a photo of a penis and professor John Schindler's name atop it was circulated on Twitter early Monday. It was unclear who sent it and who posted it.
A blogger sent a complaint to the War College's administration. The college's president, Rear Adm. Walter E. "Ted" Carter Jr., ordered an investigation. A college spokeswoman said investigators would look into whether the photo could have been falsified.
Schindler refused to discuss the photo by telephone on Monday, citing legal reasons. He has deleted his Twitter account.
Schindler is a professor of national security affairs and a former National Security Agency intelligence analyst. He has been critical of leaker Edward Snowden and others and frequently engaged in heated exchanges with critics on Twitter.
On his website, he wrote on Monday that he has been subjected to "nearly non-stop online harassment and stalking" for the past year and "things have now taken an ugly, indeed sordid turn." That post was later replaced with a much shorter statement, telling supporters he is taking a break from social media because of personal issues.
Schindler has taught at the college since 2005. He also is a fellow at Boston University, according to its website. His resume says he was a senior intelligence analyst with the NSA from 1996 to 2004.
U.S. Naval War College, in Newport, is a one-year, resident program that graduates about 600 students a year, according to its website. It said in a statement it could not comment further to protect the integrity of the investigation. It did not say how long the investigation would take.