I read in Peter Szor's Art of Computer Virus Research and Defense that, in the past, a 16-byte malware signature was sufficient to 16-bit detect malware, but that longer signatures are necessary for 32-bit malware. I am wondering how large the typical signature is for modern malware.
What antivirus vendors mean when they use the term signature is not digital signature/hash/checksum. A malware signature here is really best described as a short program written in a domain specific language that can classify whether a file is or isn't malware. It does not necessarily have a specific length to it, but rather depends on the complexity of distinguishing it from legitimate software.