GPUs and online user tracking
In a research paper titled “DRAWNAPART: A Device Identification Technique based on Remote GPU Fingerprinting”, researchers have presented a method of identifying users based on browser fingerprints generated by GPUs.

These days users can be tracked by cookies, browser user-agents, network IPs, mouse movements, and other techniques. User identification is required to prevent bot network attacks but also to track users and record their preferences to serve more accurate advertisement. Where law applies, publishers are required to take consent from users



