Although it is generally not advised to install multiple anti-virus products to your computer simultaneously and the AVG website does list some incompatible programs, AVG 2011 and 2012 are compatible with other security products, including some made by Norton. However, you may still experience some unwanted behavior or conflicts.
When installing AVG security products, you will not be forced to uninstall other security products as is the case with programs such as Trend Micro. However, the website recommends that you do uninstall other anti-virus and security software just in case. AVG provides links to removal tools for individual programs because anti-virus programs can be difficult to remove.
Possible Side Effects
If you run Norton anti-virus products and AVG software concurrently, your computer may slow down and experience lag. If the programs require more resources -- processor power or memory -- than your computer has, you may also experience freezing. Lastly, AVG warns that another virus program, such as Norton, maybe block the removal of a virus even if AVG can detect it.
Aside from uninstalling AVG when installing Norton, or vice versa, consider using only one program's real-time protection and the other for scanning only. You can also temporarily disable your AVG or Norton product to allow the still-running program to complete virus scans and removals if you find that there is a conflict when both are running.
Although both AVG and Norton offer anti-virus products, they also offer stand-alone protection that may not conflict. For example, AVG's PC TuneUp is intended to boost the performance of your internet and computer but does not provide real-time virus protection. Norton Utilities is a similar product. However, if you purchase AVG or Norton Anti-virus, which are stand-alone products, you may experience conflicts. The same rings true for Norton 360 and AVG Internet Security, which are suites that include anti-virus protection among other features.