In Windows XP there is an account which is termed as Guest account and it has limited privileges. The user who is logging through guest account, generally don't have any user account. Guest account provides limited access to the computer. But there is a security issue and that's why its sometimes dangerous for any computer.
But unfortunately, Guest account is disabled by default. If you want to ensure security, it's a good practice to disable guest account and create an user account to use.
Enable or Disable Guest Account:
1. Click on Start menu--> then click on Control Panel--> double-click on User Accounts.
2. User Accounts window will be displayed and you will see a user account named as Guest.
3. By default--> Guest account is disabled--> To enable it--> click on it.
4. The new Window will displayed the following message--> Do you wnat to turn on the guest account--> Select Turn On The Guest Account--> Now the Guest account will be turned on.
5. To disable Guest account--> click on the Guest icon to access What do you want to change about the guest account--> click on Turn off the guest account.
6. close User Accounts window and Control Panel Window.
Click Here: To Enable/ Disable Guest Account In Windows 7