Did you ever had the need to search for a person's activity on internet if you his email-address?
Well, this was certainly possible in the 90s era on internet where most of the sites had exposed the email addresses of its visitors, commenters and other users. But with the inception of spam, almost all of them have closed the email address exhibiting to save its user base from being exploited and send unsolicited mails.
Today, people are connected to each other through social networks and are able to keep track of their friend's activities on internet through facebook's (a social network) 'LIKE' button and other activity update features.
But this feature only lets you find the activity if you are a friend of that person. What should you do if you are not a friend and want to know the person's activity on various sites outside the social network?
Well, some intelligent guys thought about this scenario and created a concept of exposing the email-ids of people on internet using SHA1 hashing technique.
SHA1 hashing is a security technique in which the person's email ID is converted into a long string of characters and is irreversible. Meaning that if you know the SHA1 hash of a person's email ID, you cannot reverse engineer it to find his email ID therby making the email-IDs safe from spammers.
The concept is achieved in reality using the FOAF and SIOC documents. These documents contain the SHA1 hash of the email ID and are available for Google for indexing.
For example, if you would like to search for my activity on internet, you can use my email IDs hash :
6f2dedca82439b0a4721eeb3d7cf0f92cb7b8402
on google and you will be shown the pages where i have been commenting or participating in any online discussions or have web presence.
You can create your email IDs hash here and search on Google to see your own online activities.
Please note that you will only be able to see the links of websites which support FOAF and SIOC standards and are indexed by Google. So, you are never guaranteed to get the whole set of a person's activity on internet using this method but you can certainly find at least one link to the person if you have lost him somewhere!!