Almost all browsers require certificates be recorded in Certificate Transparency logs <https://en.wikipedia.org/wiki/Certificate_Transparency#Manda...>. Since those logs are empty in this instance, you can state that no one used a forged certificate with a mainstream browser, which is the most obvious (and desirable) attack type.
Mainstream browsers were a juicy but also a very short term attack target.
The more interesting targets will be various REST etc apis being called over https. Lots of people doing API clients have been ignoring the "what if someone tricks me to connect to an evil server" vector, because they assume TLS verification will protect them.
Can anyone sign certificates with the compromised keys and submit them to a CT log?
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