I've never run into this problem with Google before, and now I've run into it twice within a half hour:

We're sorry...

... but your query looks similar to automated requests from a computer virus or spyware application. To protect our users, we can't process your request right now.

We'll restore your access as quickly as possible, so try again soon. In the meantime, if you suspect that your computer or network has been infected, you might want to run a virus checker or spyware remover to make sure that your systems are free of viruses and other spurious software.

We apologize for the inconvenience, and hope we'll see you again on Google.

To continue searching, please type the characters you see below: [fill-in blank]

Both times I was using Firefox on my Mac and doing a basic search from the search bar. Weird.