What exactly does "your IP address is being used by another device"

Question

everything is in the question, I recently had to deal with hacking attempts by e-mail, that's why I pay attention
thank you

Answer 1

Most likely, you're getting a network address from your router. The address assignment ("lease") expires, and has to be renewed, after a certain amount of time, which might be one hour or one day. The lease expired without being renewed because the device was offline at the time. Meanwhile, the address was leased to another device on the network. When the first device comes back online, it still has the address that's now also leased to the second device. Depending on what kind of router you have, the conflict may resolve itself automatically. If not, then from the menu bar, select
           ▹ System Preferences ▹ Network
If the preference pane is locked, click the lock icon in the lower left corner and enter your password to unlock it. Then click the Advanced button and select the TCP/IP tab. Now look at the menu labeled Configure IPv4. If the selection in that menu is Using DHCP, click the button labeled Renew DHCP Lease. Test.
Less likely, you have a network address that you assigned yourself, and another device is assigning itself the same address. In that case, the selection in the Configure IPv4 menu will be either Manually or Using DHCP with manual address. This kind of conflict won't be resolved automatically. You have the following options to resolve it:
Change the menu selection to Using DHCP.
Change the manually-assigned address to one that isn't being used by another device.
Change the address of the other device.
Which of these options you should choose depends on the details of why you're using a static IP address. Any change you make to the network settings must be applied before it takes effect. To do that, click OK and then Apply.