I dont think you will get infected…

If this is the usuall fake scan page it is some java thing that is doing a fake scan and ask you to download and install a program.
If you say yes you get a download that you save and then you just close the browser…
do NOT run the file downloaded but send it to avast…

found a picture of it here
http://photobucket.com/images/fake%20scan%20progress/
http://media.photobucket.com/image/fake%20scan%20progress/appleoddity/Fake-Scan.png?o=1