DraKuL
2
Its just their personal preference… Maybe they are trying to promote another antivirus product? (If you ask them to recommend a good product they will name that one), so whatever the antivirus you have installed they will say its not good unless you have the one that they are trying to promote… You have nothing to worry about, Avast! is one of the best there is 
Also may I ask which version of Avast Internet Security you have installed? If its a really old version they might be correct, Install version 6.01000, since you have purchased a license its free to update the software…