Geez, this is pretty scary especially for a newbie like me. Seems you have to have all kinds of degrees to ever feel safe online at all! I can barely wrap my mind around some of the basics to get going let alone all this techy stuff! Please! I'm already drowning in information overload - not sure I can even think about this side of it. I'll never get off the ground at this rate! Two steps forward, 50 steps back!!!! Who ever said making money online is easy???
Actually, this is pretty serious issue. Lots of sites (millions) are vulnerable. Hackers has automated tool to infect such sites (SQL injections are very wide spread lately). As a result legitimate sites silently distribute malware (trojans). Google detect such site and ban them. I recently checked one such site. It contained AdSense code but the ads wouldn't show up because the site was blacklisted. So be warned. If your site has security issues it may cost you search engine traffic and AdSense revenue.