You are "Suffering from Scoping". (As well as two rather nasty side-effects of references, but those'll get fixed.)

Let's diagram what you're doing with @cname. You've declared it at the top of your program. This implies that you are attempting to gather together a list of computer names from across your entire file. This doesn't sound like what you want to do.

Instead, you want to gather a list of the computer names for a given IP address. Again, you're almost there.

  push @{$data{$ip}{cname}}, $1
    if /\b$ip\b\s{2,}(\w[^\s]*|\[Unknown\])\s{2}/;
  push @{$data{$ip}{ports}}, $1
    if /((\d{1,5}?)\s{2}(\w[^\n]*))\s{2}/;
  push @{$data{$ip}{banners}}, $1
    if /\Q|___\E\s+([^"]*)\.{1,3}\s+\n/;
[download]

This way, you're doing the pushing onto the array you actually want. (Obviously, you remove the declaration of @cname and his friends, cause it's not needed anymore. You also remove the hash-slicing cause it's also not needed anymore.)

For your personal edification, what was happening was that you were creating one array - @cname. Every instance of your data was referencing this specific array. Every time you modified it, each instance would know about the modifications. Every time you de-referenced it, you were de-referencing the same array.

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.