BlueStacks is for emulating an android phone on a PC. It's not a remote desktop app, and regardless such apps can't be used to control iPhones due to the way iOS sandboxes applications from the system.
Either way, all such apps need to have connections approved by hand on the device they're connecting to. I think Occam's Razor applies here- is there really a world-class hacker breaking into your phone using crappy, easy-to-spot remote desktop software? Or is there a simpler explanation?