Erdogan says this is all a conspiracy against his government. And many do believe that the probe was instigated by members of the so-called 'Gullen Movement' a very, very influential moderate Islamist movement headed up by Fethullah Gulen, who of all things lives in voluntary exile in Pennsylvania.
I follow Turkish politics somewhat closely. But I don't know nearly enough to tell you who's behind what or whether the corruption allegations are valid. (Remember, often people will try to destabilize a government with corruption charges that are valid but which focus on corruption that has in the past been routinely ignored.)
What I can tell you is that this is being widely interpreted as a battle between these two different Islamist movements in Turkey - Erdogan's AKP ruling party and the Gullen Movement. They've been rivals but often de facto partners in bringing to heel the power of the country's secular elite, embodied in and centered in the armed forces. But with that force essentially tamed, this conflict appears to be coming out into the open and perhaps threatening Erdogan's government and power.
We'll be writing more about this. And I'd love to hear from knowledgable Turkey watchers with your sense of what's going on.