Round 2 Teaser

Two steps by four is the way that I walk,

In skies you may find the prey I don't stalk.

From corner to corner I spread silken homes,

On most every landmass my brethren can roam.

There's no crack or crevice that I cannot reach,

Hidden I'll stay - my sight makes you screech.

Some of my kind earn our vile reputation,

Many of us are no murders' causation.

"But where is the teaser?" I hear you all cry!

Question for a question: what class am I?