The only thing I could come up with was self reproducing code like a virus

Well, it is used effectively as a comedic device in source filter joke modules - such as Acme::Bleach and Acme::Buffy.

The Acme::Bleach source is short and amusing (note the use of 0/$0 below to bleach the source file):

package Acme::Bleach;
our $VERSION = '1.150';
my $tie = " \t"x8;
sub whiten { local $_ = unpack "b*", pop; tr/01/ \t/; s/(.{9})/$1\n/g;
+ $tie.$_ }
sub brighten { local $_ = pop; s/^$tie|[^ \t]//g; tr/ \t/01/; pack "b*
+", $_ }
sub dirty { $_[0] =~ /\S/ }
sub dress { $_[0] =~ /^$tie/ }
open 0 or print "Can't rebleach '$0'\n" and exit;
(my $shirt = join "", <0>) =~ s/(.*)^\s*use\s+Acme::Bleach\s*;\n//sm;
my $coat = $1;
my $pressed = '#line ' . ("$coat\n" =~ tr/\n/\n/) . ' ' . (caller)[1] 
+. "\n";
local $SIG{__WARN__} = \&dirty;
do {eval $coat . brighten $shirt; print STDERR $@ if $@; exit}
    unless dirty $shirt && not dress $shirt;
open 0, ">$0" or print "Cannot bleach '$0'\n" and exit;
print {0} "${coat}use Acme::Bleach;\n", whiten $pressed.$shirt and exi
+t;
__END__
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