U.S. cyber forces conducted a secret global operation to remove pro-ISIS propaganda and videos from their host services, including those physically located in allied countries, the Washington Post reported on Tuesday.

The campaign, named Operation Glowing Symphony, began under former President Barack Obama and spurred debate among government officials as to whether the U.S. has an obligation to provide ally countries with advance notice before removing content from servers based in their territories, the report states.

Even as U.S. Cyber Command claims success following the operation, President Donald Trump's administration now inherits this ongoing debate. On one hand, failing to alert an ally could harm future cooperation in cyber investigations; on the other hand, involving additional parties increases the odds of a leak that could tip off intended targets.

The classified operation, which was executed from November 2016 into the next year, consisted of U.S. Cyber Command personnel accessing ISIS admin accounts using stolen passwords, then deleting the content and changing the passwords so that the original account holders could no longer use them, the Post reported, citing former officials. Ultimately, the U.S. reportedly gave advance warning to 15 countries, but only accessed accounts hosted in five or six countries.

“It's a tricky thing to navigate,” said a former U.S. official quoted in the report. “Think how we would react if one of our allies undertook a cyber operation that affected servers here in the United States without giving us a heads-up.”