Visit:

http://www.computerbild.de/gutscheinaktionen/Avast-Internet-Security-2016-Verlosung-14384121.html?action=register

Enter your email (it can be a disposable email if you want)
Do the captcha
Click "Jetzt Avast Internet Security 2016 gratis anfordern"
View your inbox
You will see 2 emails from them - The first has the code in it

You're welcome

I've tried it but received only 1 email without the code.

Me too... Whats happening? Huh

I think we missed the promotion was only November I think