Strange Google error: "your query looks similar to automated requestsfrom a computer virus"

I am getting a error when I try to use Google on Firefox. The error says that 403 forbidden. The message says that your query looks similar to automated request from a virus. I have not virus in my computer. I am using AVG as antivirus and this message has started appearing from today morning. I am scanning my system but nothing is detected. How can I fix this thing. Thanks.

Try to remove the browser and install it back again. And test the same on other browsers also. I hope you would not get the same error on other one. If still then you have to contact your ISP for the issue. There are chances that your IP address is being compromised.