A 404 error – “Not Found” is when a URL on a website or a resource such as CSS file or image cannot be found. This could be because of a typo in a URL, a programming error or perhaps the file was deleted. No matter the reason, when a file cannot be found, a 404 – Not Found message will be displayed.
Are 404 errors dangerous for my website?
Yes, but how much depends on how many and how prominent they are. Not only does 404 errors give a bad user experience for your visitors, but it also shows Google and other search engine crawlers that you have mistakes on your website that you do not fix, and if they continue finding a lot of 404 errors, it will give a negative impact. It can also mean an increase in server resources because it takes processing power to make a request to a URL that does not exist and it also takes up extra resources serving different files to display the 404 error page. That being said, 404 errors are also a way of making sure Google search robots eventually forget about your old URL if you want it to be gone from their index and search results. This could happen if your website is hacked and you used 404 errors as a way to clean old spam-injected hacked URLs (sigh, I hate cleaning that stuff up).
I have many 404 errors!
Don’t worry. It is sometimes easy to fix. Sometimes an hours work is enough to clean any decent size website of hundreds of pages. Use the report from the 404 errors page in SEO Booster Pro Disclaimer – I make the plugin, and you are right here on the same website reading about it. If you use WordPress you should take a look; it does a lot of other very cool things.
Personally, I like and regularly use the WordPress plugin Redirection by John Godley.