Retroactive malware protection can help protect the user by checking a user’s
browsing history. If a site in the user’s browser history corresponds to a newly
identified malware site, the user can be notified. Checking the user’s browser
history against an updated malware database can be done locally or remotely. The
functionality of the system may be implemented, for example, in the browser itself,
as a browser extension or plugin, or embedded within a web site or web application.