The subject line said “Bomb,” and the email — sent to more than 600 current and former students at one of the District’s best-regarded charter schools — appeared to come from a Muslim student’s account.

But the message was in fact written by two pranksters, school officials said. The two boys, both high school seniors at high-performing Washington Latin Public Charter School, were expelled for threatening violence, said Head of School Martha Cutts.

“I was never really worried that it was a real threat, but you have to obviously take those things very seriously,” Cutts said. “It can be very unsettling for students to open an email and read that.”

The email was sent Wednesday, and it was short: “Friday there will be big boom.”

Terror attacks in San Bernardino, Calif., and Paris have put many schools on edge. Several Boston-area schools were evacuated Friday after receiving bomb threats via telephone, Reuters reported. In December, an emailed threat of violence prompted Los Angeles Unified — the nation’s second-largest school district — to take the unprecedented step of shuttering schools for all 650,000 of its students. Later that month, a much smaller district in Nashua, N.H., canceled classes for the same reason.

The incident at Washington Latin was a case not of hacking but of opportunistic identity fraud, Cutts said. A pair of students opened a laptop during class time and discovered that a previous user — a student who happened to be Muslim — had failed to sign out of his school email account. They sent the short email to students in grades eight and above, as well as two classes of alumni, Cutts said.

Potential mischief-makers, take note: School administrators quickly were able to figure out which laptop had sent the message and where that laptop was located when the email was sent. Armed with that information, it was not difficult to figure out who was to blame.

The Muslim student is fine, Cutts said, and received a lot of support from other students.

Ibrahim Hooper, spokesman for the Council on American-Islamic Relations, said CAIR has seen an increase in bullying of Muslim students in recent years. He said the email should be considered anti-Muslim bullying and a hate crime.

“It’s based on the overall atmosphere of Islamophobia in our society,” Hooper said. If the students weren’t “hearing and seeing this kind of anti-Muslim sentiment in their daily lives, they wouldn’t have even thought to use a Muslim student’s email account to send a bomb threat.”

He said anti-Muslim incidents have spiked since the Paris and San Bernardino attacks. He blamed the anti-Muslim rhetoric of Donald Trump and other politicians that he said have helped make Islamophobia part of mainstream culture.

“It’s been a really bad few months,” he said.

The two boys were expelled, and Cutts said that whenever she has had to expel a student, she speaks to the school to explain — without mentioning names — what happened and what the consequences were. “These are absolutely teachable moments,”  she said.

One important lesson from this particular incident? Shut down your email account when you’re finished.

But the email threat also was a perfect example of the power of words and the need to use them wisely and respectfully, Cutts said.

“One of the things we say at our school,” Cutts said, “is words matter.”