[dogscoff]

Is there a chance that someone can built it so early?

Maybe... it would be very difficult, but maybe. To have lvl3 cloaking tech *as well* seems unlikely. You imght want to drop a few mines around your stars, just in case.

As for detection...

Cloaking devices and natural cloaking (ie storms) *do* stack - ie if your sensors could see through his cloak *or* a storm, he could theoretically be able to hide from you by combining the storma nd device cloaks.

Still, sounds like a bluff to me. Don't blame me if your system gets detonated, mind...