A new Pentagon report found that roughly 100 U.S. service members participated in "prohibited extremist activities" in the last nine months.

"We believe that less than 100, or about 100, active duty or reserve component members of the military participated in prohibited extremist activities," Pentagon press secretary John Kirby said during a Monday press briefing, adding that the military's "data collecting systems still need to get better."

The number represents just a fraction of the over 2 million people who currently serve in the U.S. military, with Kirby saying the "vast majority of men and women in our armed forces… serve honorably."

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Pentagon spokesman John Kirby.

Pentagon spokesman John Kirby. (AP Photo/Alex Brandon)

Kirby's comments come after the Department of Defense Monday released its report, "Countering Extremist Activities," which was ordered by Defense Secretary Lloyd Austin earlier this year after it was found many of the participants in the Jan. 6 Capitol riot were active military or veterans.

The report outlines next steps to combat extremist activity in the military, detailing certain extremist activities, including advocating terrorism or supporting the overthrow of the government, that are prohibited for service members to engage in.

Trump supporters try to break through a police barrier on Jan. 6, 2021, at the Capitol in Washington. (AP Photo/Julio Cortez)

Trump supporters try to break through a police barrier on Jan. 6, 2021, at the Capitol in Washington. (AP Photo/Julio Cortez)

Service members could also land themselves in trouble for "liking" or sharing extremist content on social media, though Kirby said there was no monitoring system in place, and enforcement of the rule would depend on leaders discovering the activity.

The new strategy does not change what is a prohibited activity for military members but seeks to give more detailed definitions of what does and does not constitute extremist activity.

In order to hold service members accountable for engaging in extremist activities, commanders are required to determine whether two criteria are met. First, the commander must determine service member's actions meet the definition of extremist activity. Secondly, it must be determined that the service member "actively participated" in the prohibited activity.

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Secretary of Defense Lloyd Austin

Secretary of Defense Lloyd Austin (AP Photo/Alex Brandon)

But the report did not designate specific groups such as Proud Boys or Black Lives Matter as extremist groups, an omission Kirby said was deliberate despite widespread attention on the issue.

"Groups can and do change their methodology, their ideals, their motivations, and they can reform themselves," Kirby said. "They can disband and reform into something else. And so if we got into coming up with a list of extremist groups, it would be only probably as good as the day we published it."