Generally uncountable nouns in english are treated as singular, even if there is more than one. "All the software is corrupted" or "All this flour is heavy!" Malware is not really considered countable since it isn't really referring to a number of installations but more of an abstract concept. If you meant to say that the different malware programs are more and more sophisticated, you could do so, because then you're referring to "programs" which is countable.
This as opposed to countable nouns which are treated as singular or plural, even when the plural form is irregular. "All the sheep look sick" or "The moose all have thick fur"