[yilmaz]

Only thing you can do to prevent this in vBulletin is to make sure that Persistent Connections in vBulletin's config.php are turned off. Other than that you'll need to purchase a plan with more connections from your host or move to another provider.

The section in the config.php file is:
// ****** MASTER DATABASE PERSISTENT CONNECTIONS ******
// This option allows you to turn persistent connections to MySQL on or off.
// The difference in performance is negligible for all but the largest boards.
// If you are unsure what this should be, leave it off. (0 = off; 1 = on)
$config['MasterServer']['usepconnect'] = 0;

This should be set to 0 in your file.