I think my computer may be infected?

Hello Sarah.
Please note that these kind of tool bars and search engines get into the computer along with some other software or if we visit any untrustworthy websites accidentally. I would request you to uninstall unknown add ons from your web browsers. Please right click on the desktop shortcuts of your web browsers, click on Properties, check the 'Target' field. It should be “C:\Program Files\Internet Explorer\iexplore.exe” for IE and “C:\Program Files (x86)\Google\Chrome\Application\chrome.exe”  for Chrome. Please check and remove if any other text is added to this path. Thank you.

1) I think my computer may be infected. When I click on a Google icon it comes up with a spurious search engine. I have been warned about this and wondered why my AVG protection didn't pick it up?
2) I have also had a warning about an AVG add-on. It came from my Avast programme. What do I do  please? 

Sarah, AVG & Avast… You shouldn't have 2 anti-virus progs… installed on the same system.
AVG Guru