99% types of malware is known by avast?

Viruses and worms
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Please read subject!

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And your question is ?

Since there is no way of quantifying this, no one can say one way or the other.

On a recent anti-malware test avast got 99.2%, but that is of the malware in the test, so as I said no way for any AV to make that claim as it can’t really be verified.