If not a full-scale invasion, what might a Russian attack on Ukraine look like? We've seen it before.

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.