That means there are 10 * 9 * 8 * 21⁴ = 140,026,320 different identicons that can be generated, so Nimiq is capable of generating more than 100 million highly differentiated and instantly recognizable identicons. This protect users against malware and clipboard hijacking.
Yeah sure. It takes 5 minutes to do a full vanity search of 140,026,320 taking into considerations all possible colors and body parts. So, any "hacker" can generate an identical (identical!!!) identicon in a few minutes.
On bitcoin, a Core i7-4702MQ 2.2GHz (very old cpu), it scan (CPU only) 1.10 mkey/s. So, it would take 2 minutes to generate an identical identicon.
So your identicons really really suck breaching its security than any other solution.