Learn Spanish (Latin America): Llevamos dos días investigando ese ciberataque. - We have been investigating that cyberattack for two days.

In Spanish, the most natural and idiomatic way to say you have been doing something for a specific amount of time (and are still doing it) is the structure llevar + time period + gerund. While hemos estado investigando por dos días is grammatically understandable, native speakers overwhelmingly prefer the llevar structure for ongoing time frames.

The current lesson is about the state passive (estar + past participle). Could we describe this situation using estar investigado?

No, because the state passive strictly describes the completed result of an action. Since we are still actively looking into the attack right now (investigando), the action isn't finished yet. You would only use the state passive once the case is closed and you want to describe its resolved status: El ciberataque ya está investigado (The cyberattack is already investigated).

Is there a preposition missing? In English we say "for two days", so shouldn't there be a por or durante before dos días?

When you use the llevar + time + gerund structure, you do not use a preposition like por or durante before the time period. The verb llevar in this specific construction already inherently covers the passage of that duration.

Why is it ese ciberataque and not eso ciberataque?