Google sometimes displays a CAPTCHA page when it notices unusual Web-searching traffic. This page forces you to enter a displayed code on your screen to confirm that you're not a program but rather a human being, before you can continue using Google. Automating Google searches is against Google's terms of service, and creates unusual traffic that triggers the CAPTCHA. If you frequently encounter the Google CAPTCHA, a program running on your computer or another computer on your network is likely performing automated Google searches. This may be a virus or other malware program, or just a program that's performing automated searches in violation of Google's terms of service.
Perform a scan for viruses and spyware on your system using your antivirus or antispyware program. If you don't have a program installed, download and install a free antivirus product such as Microsoft Security Essentials from Microsoft.com, AVG Free from free.avg.com or Avast! from Avast.com.
Run antivirus programs on other computers on your network. If you don't have access to other computers on your network, contact your network administrator with information about the problem. Automated programs running on any computer on the network can trigger the CAPTCHA for the entire network.
Disable any programs that run automated search queries to determine a Web pages' rank, save search results pages for use offline or run several search queries in a short amount of time. These programs must be disabled both on your computer and on any other computer on your network.
Open the "Connecting to Google: 'We're Sorry' Page" page on Google.com/Support in your Web browser and fill out the form to request Google look into your problem. Google may fix the problem if the CAPTCHA is being displayed in error.
Any unusually large amount of search queries in a short amount of time may look like the work of a software program and trigger the CAPTCHA.