That's your Network shiled alarming you (better to say, informing you) about possible exploit. That means your Network shield works great...
See attachment how can you disable showing that message. Your Network shield will be still active, but you won't get those messages on the screen if you are annoyed by them...
Go into avast! On-Access Scanner, choose your Network Shield, and click on CUSTOMIZE button. You'll get window like this one on the screenshot. Uncheck first option and click OK. Note, that I said UNCHECK, so it shouldn't be checked like on my screenshot if you don't wanna see those info messages...
Cheers !