I don't think we need to suspect the RAR encryption is broken. By default, at least on Linux, even if an archive is encrypted a 'rar l <file>' will show a file list though. So if the files had relevant filenames like mybitcoins.txt then it made searching the harddrive for money easier. At least I suspect crackers look for files called creditcards.txt, passwords.txt etc.
If the crackers knows the archive contains coins, then bruteforcing is worth it.
Comments
I don't think we need to suspect the RAR encryption is broken. By default, at least on Linux, even if an archive is encrypted a 'rar l <file>' will show a file list though. So if the files had relevant filenames like mybitcoins.txt then it made searching the harddrive for money easier. At least I suspect crackers look for files called creditcards.txt, passwords.txt etc.
If the crackers knows the archive contains coins, then bruteforcing is worth it.