Well, you're redefining your hash every time you are in the loop, so it's local to the loop. And you're also using a string "key" to be the key. What do you want to be the key? Uip? and the value to be Uuser? If so...

my $hash;
while ($WOW =~ m!<table id=.*?table.*?<a href=.*?><b>(.*?)</b></a></sp
+an>.*?\(from (.*?)\)!sim) {
  $Uip = $1;
  $Uuser = $2;
  $hash{$Uip} = $Uuser;
 ...
}
foreach my $key ( keys %hash ) {
  print "$key is Uip and $hash{$key} is Uuser\n";
}
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