Ever conduct a search at Google and be presented with a "We're sorry" error from Google? The image on the right is what you would see and Google thinks you are a machine conducting automated queries and they want to validate you as a human.
Well, over the past few days, I have been noticing a much larger number of threads with complaints from searchers that they have been getting this message. I typically see threads on the issue but not the number and volume I have been seeing over the past few days.
I then spotted a Google Web Search Help thread that has confirmation from Google that this is an issue on their side. Skylar from Google said:
Hey! Thanks y'all for sharing this strange behavior in your Google's search results. This is an issue (we're working on it) caused by computer worms that search for vulnerable sites to infect. These nasty annoying computer worms will use certain search queries or patterns to find those sites. When we detect these abusive queries, we display the 'We're Sorry' page to stop the worms. Once in a blue moon, your search queries can coincidentally match the search patterns that worms use, and you get blocked as a result.
A quick fix you could try is simply adding another key word to make your search queries more unique (and different from the queries worms use). By making this change, you're less likely to be blocked. Check out http://googleonlinesecurity.blogspot.com/2007/07/reason-behind-were-sorry-message.html to read an interesting blog post on reasons behind the 'We're Sorry' page.
So it seems like Google is aware of showing this message to real humans, a bit too often and they are working on a fix.
Forum discussion at Google Web Search Help.