Hello menestrello,

Please accept our apologies for prolonged answer.

The use of more than one anti-virus program on a single computer is generally not recommended by any security software provider. This does not provide any additional protection, but instead may cause conflicts in their main components. These conflicts could cause unexpected failures on the system and prevent the programs from working properly.

Avira FAQ:
http://www.avira.com/en/support/would_it_be_wrong_to_install_multiple_antivirus_programs_in_parallel.html

Thank you