So how does the update to 1.0.7.9 technically work? Since it is mandatory, I thought this would mean it has some effect on the blockchain. But you said there wouldn't be a certain block, so it hasn't? That is a bit confusing, how is it mandatory then? For example the botnet could just stay on the old version and keep on mining.

On another note: just as a tip to people with more powerful machines (Ryzen, DualXeon etc.): try going solo for some days and test your luck. I have one of my Dual-Xeons (actually my weakest one...) on solo mining for maybe 5 days now (just updated to 79) and it already found 2 blocks (overall more than 10k BBP per week). Of course this could be pure luck, but it definitely is worth a shot!