[5/17/17]  The Department of Homeland Security renewed a bulletin late Monday that warned of the dangers posed by homegrown terrorists and called the threat environment in the country one of the “most serious” since the 9/11 attacks.

“We face one of the most serious terror threat environments since the 9/11 attacks as foreign terrorist organizations continue to exploit the Internet to inspire, enable, or direct individuals already here in the homeland to commit terrorist acts,” the bulletin, issued through the National Terrorism Advisory System, said.

An NTAS bulletin was first issued in December 2015 to “highlight the continuing threat from homegrown terrorists” and has been renewed three times previously with updated language.

Monday’s bulletin, which is set to expire in November, includes new warnings on the techniques used by terrorists, like car attacks, that did not appear in the previous iteration.

“Terrorist groups are urging recruits to adopt easy-to-use tools to target public places and events,” the bulletin reads. “Specific attack tactics have included the use of vehicle ramming, small arms, straight-edged blades or knives, and homemade explosives, as well as other acts such as taking hostages.”

The reference to vehicle ramming comes after a series of attacks around the world in recent months where alleged terrorists used cars and trucks as weapons. In April, a suspected terrorist killed four pedestrians on a busy Stockholm street with a hijacked beer truck.

The bulletin also includes new language describing foreign terrorist fighters who may be “attempting to travel to the United States on visas, from visa-waiver countries, with the aim of attacking the homeland or inciting others within our borders to conduct attack.”