In the free Avira Antivir Personal version when you update the antivirus an advertisement popup appears about benefits by upgrading it to the Premium version.
There are 2 ways to disable that popup, manual method (for Windows XP and Vista):
1. Start-> Control Panel
2. Administrative tools-> Local security policy
3. Click on Software Restriction Policy-> Action (at the top)-> create new restriction policies
4. Right-click additional rules (on the right side)-> new path rule
5. Click Browse and navigate to C:Program Files(Avira)AntiVir Desktop and double-click avnotify.exe
6. Set the security level to Disallowed-> apply-> ok
automatic method (for Windows XP):
download the program No Notify Avira, this also removes start splash screen.