Kyiv, Ukraine — The U.S. government’s warning that Russia could launch a cyberattack targeting America’s critical infrastructure likely surprised very few Ukrainians. CBS News senior foreign correspondent Holly Williams and her team have been reporting on Russia’s aggression in Ukraine — in its many forms — since Vladimir Putin’s forces last invaded in 2014.

Russia’s buildup of about 100,000 troops around Ukraine’s eastern borders has fueled fear of a full-scale invasion. Stressing their unity, the U.S. and its European allies have issued increasingly stark warnings that any Russian forces crossing the border would bring “massive” and “severe” consequences for Putin’s government. 

But Williams’ reporting on the war that has simmered quietly for seven years on the fault line between Russia and the democratic West shows Putin’s tactics are often obscured. The question for Ukrainians now is not just if Russia will attack, but how.

As NATO deployed fighter jets, troops and ships to reinforce defenses in Eastern Europe, Ukrainian President Volodymyr Zelenskyy addressed his people on Monday evening. He urged them not to panic.

Russia still insists it has no plans to invade Ukraine. The Kremlin blames the U.S. and NATO for causing the current crisis. Putin’s spokesman pointed on Tuesday to the Biden administration putting 8,500 more troops on a state of heightened alert, ready to deploy to Europe if needed, as another “escalation of tension.”

But Russia has invaded Ukraine before, seizing control of the Crimean Peninsula in 2014. That experience, and Russia’s actions since, have drawn warnings from the U.S. that Moscow could rely on more secretive tactics.

“Paramilitary tactics, so-called gray zone attacks, and actions by soldiers not wearing Russian uniforms,” said President Biden last week.

Russia already stands accused of that in eastern Ukraine. Williams and her team witnessed first-hand Russian-backed separatists taking control of towns and cities in the Donbas region in 2014. That conflict has now killed more than 14,000 people.

The U.S. says Russia controls the armed rebels.

Seven years ago, CBS News saw well-equipped forces working alongside those rebels with all identifying insignia and national colors missing from their uniforms.

“I’m just a person,” one of the men told Williams when she asked if he was Ukrainian or Russian. He wouldn’t say any more.

As recently as November last year a verdict delivered by a Russian court in a bribery case appeared to inadvertently reference the presence of Russian troops in eastern Ukraine’s rebel-held Donbas region.

Moscow flatly denies the presence of any Russian forces in Ukraine. Asked about the verdict that mentioned such a presence — which was quickly removed from the court’s website — Kremlin spokesman Dmitry Peskov said it was “probably the mistake of those who wrote this text.”

Then there’s Russia’s proclivity for virtual warfare. 

Suspected Russian hackers have previously succeeded in crashing parts of Ukraine’s power grid. When one power station came under attack in 2015, nearly 250,000 people lost electricity.

The Department of Homeland Security has warned law enforcement agencies across the U.S. that Russia could target America with cyberattacks if “a US or NATO response to a possible Russian invasion of Ukraine threatened its long-term national security.”

“Russia maintains a range of offensive cyber tools that it could employ against U.S. networks — from low-level denials of service to destructive attacks targeting critical infrastructure,” a bulletin issued Sunday by DHS warned.

There is still hope that diplomacy can resolve the tension, however. 

Ukrainian and Russian officials will meet in Paris on Wednesday, along with their French and German counterparts, and Putin was to speak directly on the phone with French leader Emmanuel Macron in the coming days.