Recently several companies have developed features or products to make web surfing more secure. One of these technologies uses reputation. Reputation is a measure of trust for a web site or web page. In this case trust is typically measured by how much SPAM, malicious traffic, or attacks a site is known to generate. It turns out that measuring these things is not that hard because a majority of web traffic flows through a relatively small number of gateways and backbone networks.
This is a very good idea. If a web site is known to host malware or send a lot of SPAM, then block or warn users before they visit a site. Of course, cyber-criminals have started to figure out how to bypass these checks. They simply attack sites with good reputations and get them to host the malware. In some cases, it's just a matter of providing an advertisement.
Reputation based security is still a great idea because it forces the crooks to work harder. However, we can't get over confident and rely on this technique to always protect us. This means keep your software patched, don't click on suspicious links, and ignore any offer that is to good to be true.