On Sunday, developer Jesse Li described a novel method to detect when Chrome users have activated Incognito mode using Chrome's FileSystem API: it is possible to benchmark the speed at which files can be written to disk using this software interface.

The technique is similar to one proposed last month by security researcher Vikas Mishra. He found that browser's Quota Management API, for managing temporary and persistent storage, can be used to infer the presence or absence of Incognito mode.

Incognito mode in Chrome sounds as if it keeps users anonymous online. But it doesn't. It simply prevents browsing activity from being stored in the History log and it erases local HTTP cookies and site data from memory when the Incognito session ends (rather than writing the data to local storage). Its purpose is to prevent other people using the same browser on the same device from being able to look at an in-browser record of past browsing sessions.