The installation of product updates like the service pack 2 for AntiVir 10 and the behavior can be configured by different settings.
For a better visualization we have composed a spreadsheet for you:
Click here to open the sheet.
You can find illustrated HowTos for various update-scenarios in the following articles:
Avira AV 10 Service Pack 2 Update Standalone HowTo
Avira AV 10 Service Pack 2 Update via SMC HowTo.