Google has programmers whose job is to block websites with malware. They do their work by entering dangerous websites into a registry for Google to block. The computer than warns users of the dangers of accessing such a site, and won’t let them on the site.
Basically, once a website is on Google’s malware registry, no one will ever see the site again. The problem came when one of programmers entered just a slash into the registry (/). As you will notice, every website address contains slashes because they are pretty much the punctuation of web addresses.
Since the slash was on the registry every website in the Google index was blocked including Google websites. It was a horrible mistake that, in effect, stopped the Internet for working for 55 minutes until programmers fixed the error. Google quickly admitted their mistake and apologized for the error.
Few remembered it after that sad, Internet-free morning in 2009. It does show, however, how huge a problem the slightest error can make. It only takes a small detail to completely derail the Internet!