Google has decided to retire Web alerts and introduce 'Everything Alerts' instead.
Google has decided to retire Web alerts because (1) they are used by very few people and (2) an alert of type Everything will find the same results.
This week we’ll be changing all alerts of type Web into alerts of type Everything. Your alert will continue to include results from all kinds of web sites.
You may receive more results after this change. If you find that you are getting too many results, you can change the “How often” setting to “once a day” or “once a week.” You can also change your search query. You can do this on the alerts management page (www.google.com/alerts/manage), or by removing the alert using the link at the bottom of each alert email and creating it again with different settings.