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1. What if I am temporary disable Avast while installing software then the software put virus/malware while installing into my computer without my knowledge.
2. If this happened, and then i start scanning its possible Avast detecting this virus/malware even though this virus infected my computer while avast disabled ?
1. What would you want to temporarily disable avast for, this really is what resident antivirus software is designed for.
I rarely if ever disable avast to install a program - many, many years ago this was suggested by many pieces of software and I would have to wonder as to their reason for this. I would rather look for a different software option if that was what they wanted.
2. It would really depend on what that virus, malware was, so there could be no 100% guarantee it would be caught on subsequent scans.