since i’ve avast!: no problem.Before i had bitdefender pro,it said me "“you’re infected. bye-bye!!!”
so,i’me very surprised by some intervenants on this forum,with their problems with avast!it is truly wonderfull,and i advise it to all my friends.It’s the first time,i leave my son surf on the net ,calmly;thanks to avast!
Welcome to the board. It’s nice to have another Avast user who likes it.
Just some words of advise.
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Avast like every other av application can’t detect all malware. When in doubt or want to be sure, you can also use JOTTI in addition to Avast.
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Security (being safe) is not only a matter of having properly installed/configured av software. A firewall is also a good thing to have.
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safety begins with the user! Have a look at THIS THREAD for some info/tips/tricks.
You can also get more security related utilities here: www.security-ops.tk
You may also try my avast! External Control if you need anything to tweak 
Welcome to the forums.
I think many users don’t take the time to get to know the programs that they use (not just avast), a little time spent reading help files (RTFM, F=flipping), etc. gets the most from the program, most efficient/effective settings, etc.
For most it’s when they experience a problem that they start to get religion, and RTFM. Then it’s panic stations, as this saying goes ‘when you are up to your ar*e in alligators, the last thing on your mind is draining the swamp.’
Time spent in reconnaissance is seldom wasted, get to know your software.