A backdoor is a type of computer software that is placed into the hosting computer/device without the knowledge or permission of the owner. Using a backdoor allows hackers to access a system repeatedly at their own convenience. They will use the compromised system as a base to launch attacks and infect other systems by sending out spam email and installing phishing pages.
Backdoors come in several ways including computer worms that install a backdoor on an affected PC, backdoors hidden in counterfeit software programmes and devices which have backdoors already installed. Legitimate software companies may create a backdoor on a computer or device so they can provide technical support. Unfortunately, even when a backdoor is put on your machine for good reasons, there’s a good chance a hacker will find out about it and use it against you.
Default passwords can be used as backdoors if they are not changed by the user.
Protecting against backdoors is complicated. You should have a firewall in place that can block entry points from all unauthorised users. Checking new software is important, because new software, especially from sources that are unknown or not well-known, can contain backdoors. If you are suspicious of the software don’t use it. Accept software only from trusted sources. Don’t install counterfeit software and change default passwords as soon as you receive a new system or device.