Updating known hosts
Your browser would attempt to access 127.0.0.1, your own computer, and that would fail.From this comes one ad blocking technique that places these kinds of entries into your hosts file for known advertising sites.I've looked in my "\windows\system32\drivers\etc\hosts" file and found a number of entries that all begin with 127.0.0.1. What are all those identical seemingly IP addresses, 127.0.0.1? The sites listed, are they on my system and bad or are they being blocked from my computer to reach them (just like what you had stated Sasser, sometimes does to reach Anti-virus sites for definition updates? 127.0.0.1 is "special", and refers to your own computer. The trick here is to understand which, and perhaps how these entries appeared on your computer in the first place. Shall I delete these sites and only keep the localhost line?In looking at the list provided by the person asking the question, that appears to be what's happening here.These appear to be advertising or malware sites that have been blocked. I'm going to assume that since you're asking, you didn't put it there.Now, unless you're running a web server on your own machine (highly unlikely unless you explicitly set it up), and if a web browser tries to connect to 127.0.0.1 that connection will fail - there's no web server to answer the call.The other piece of this puzzle is to realize that entries in your hosts file take priority over "real" lookups.
Your browser would request the IP address for google.com, the system would find it in your hosts file first and assume that was the correct address.Manually installing such a list is the most common approach.