Another example is SCW-3328 which allowed to remotely turn on your muted microphone during a call.
Even at that time, I was worried by Skype’s approach to fixing bugs.
It could be end-to-end encryption, but there are indications that, particularly when routed through the Skype servers, the conversation could be visible or audible in unencrypted form.
On top of that, there’s really no reliable way to tell what kind of connection you have, or even if you do have a Skype-to-Skype connection, that the information still isn’t being mirrored to Skype’s servers somehow.
Mostly the accounts were blocked via mass abuse reports.