After successful virus definition update ‘instup.exe’ process cannot close automatically. ‘Already up to date’ message in avast UI cannot disappear if I click on ‘Ok’ button several times. ‘instup.exe’ process continuously uses my data bandwidth, it is very irritating to me. But when I disconnect my internet ‘instup.exe’ process automatically close after few seconds.
I am using avast! free antivirus v11.1.2253 with virus definition version 160323-2
Perform a repair of avast and see if it solved the problem.
I have performed a repair but problem still occurs with ‘ask when an update is available’ settings of virus definition update.
What happens with other settings ?
Let me be try with other settings (Automatic update) until next virus definition release.
Tried in both Automatic & Mannual Update settings but problem sitll occurs
Only thing left to try is to perform a clean installation of avast.
If that doesn’t solve it, I suggest you send a support package to avast.
https://www.avast.com/faq.php?article=AVKB33
Thanks Eddy, I have performed a clean install & problem is solved now.
That is news I like to hear 
Take care and keep your system safe.
Few hours ago the problem arise again. Can not understand what is the actual reason…
now the problem is solved