When searching Google, you get:
Our systems have detected unusual traffic from your computer network…
This means that Google has detected traffic from a bot (perhaps virus) that is searching Google on your computer network. It’s important to be aware that this does not necessarily mean that there’s a bot / virus on your computer network, it could be any computer that shares you ISP (since this is the external IP address that Google sees).
To fix the detection of unusual traffic, run an antivirus scan on all the computers on your network (that you control). Follow the usual steps to check for viruses, like making sure that your antivirus software is up to date, working and that you have all the Windows Updates installed on your computer(s). Once you’ve done this, enter the code for the captcha to proceed.
You may later get the Our systems have detected unusual traffic from your computer network message again, but at least in future you will know that it’s not a problem with your computer and hopefully your ISP will sort the problem out soon by blocking the user with the virus / bot network.