Is there a way to clean a website infected with a virus or bad code?

[FluidArt]

If I have the wrong board, please let me know. 

I have suddenly started receiving the following message from Avast when I view my website. Does anyone know how I can clean the website please?  I assume there is a virus or some bad code on my site. 

We've safely aborted connection on googie.anaiytics.com because it was infected with URL:Blacklist. 

Thanks

Kazz