Ransom Trojans have evolved over time. The newer variants target files on a computer’s local drives, network shares and cloud paths alike.
It’s been years since it became obvious that crypto isn’t necessarily usable for benign purposes only. Back in the day, a variety of data encryption techniques were contrived to protect sensitive communication against MITM (man-in-the-middle) attacks and similar interception attempts. The creators of file-encrypting ransomware, however, have ventured to add a malicious component to the mix, using both symmetric and asymmetric algorithms to lock their victims’ data and hold it for ransom.