On level 4, it is assumed that the attacker owns a domain name. Given solutions use 2 unicode characters for the domain name, totalling 6 bytes. The actual shortest domain name in use is 'uz' (http://uz/) which is a registrar for .uz, Uzbekistan's ccTLD, making the answer shorter by 4 bytes.
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[ 2.7 ms ] story [ 23.7 ms ] threadLooks like it's not responding though.
Gets you to the same challenges.