La arroba es para evitar que muestre los errores... y quitándola da más warnings:
Warning: fsockopen(): php_network_getaddresses: gethostbyname failed in c:\inetpub\wwwroot\test.php on line 6
Warning: fsockopen(): unable to connect to
http://www.forosdelweb.com:80 in c:\inetpub\wwwroot\test.php on line 6
Warning: fputs(): supplied argument is not a valid stream resource in c:\inetpub\wwwroot\test.php on line 7
...