In this case the specific software we're talking about had a feature whose specific purpose was to detect someone entering a credit card number, screenshot it and upload the image to an FTP server:
'In further MSN chats with the FBI, the person alleged to be Hogue answered a question about whether the Blackshades software would automatically conduct key logging or whether it had to be initiated manually. "It auto does, and you can download from all at once, or scan for keywords or digits," came the reply. "And if it detects a credit card is being entered, it can send screenshots to FTP and you can scan for digits that are 16 in a row :P"'
It also had as a feature to encrypt a users files and pop up a ransom notice:
'Blackshades went beyond DarkComet in its support for features that were likely to result in illegality, such as the "File Hijacker" that could encrypt a victim's key files and then pop up a "ransomware" message demanding payment into a remote bank account in order to free the files. (A note attached to this feature said: "However, one thing to put in mind: This feature was made for educational purposes only.")'
In general, even tools that are quite clearly intended for illegal uses seems to be ok. But this one took it much further.