My phone may have spontaneously downloaded malware???

I pulled my phone out of my pocket and it had downloaded flashBrowser_Mobusi_3442.apk into my downloads folder. I have no idea how this happened. Did I pocket-download a file? What the heck? Obviously, I didn't install it.

I did a Google search and there are all these pages with technical info that implies it's bad news but i don't understand them. Maybe someone else can check? (Search here)

If it is malware....... how did this happen?? I must have accidentally done something.

(I'm running 7.0 Preview 5)