There are many websites and apps that claim to be a "Facebook Profile Picture Viewer HD" that can "unlock" private photos. Users should exercise extreme caution here: No Official Tracking: explicitly states
The term "hot" in this context often refers to trending or attractive profiles that users may have "locked" for privacy. Locked Profiles:
Some users used to bypass low-res thumbnails by right-clicking an image and selecting "Open image in new tab," then manually changing the URL dimensions (like changing /s160x160/ /s720x720/
photo looks "hot" and crisp, you must enable "Upload HD" in your Facebook Account Settings under the "Videos and Photos" section. 2. Privacy and "Locked" Profiles