DDoS attacks (Distributed Denial-of-Service attacks) have been a global Internet phenomenon and a problem for quite some time now. Ever since the Internet started being used for making money and for generating large amounts of revenue, there have been people who have been trying (for whatever purpose) to bring down these webpages.
These attacks have a final goal of stopping the functioning of a website, which will, in turn, make it inaccessible for everyone on the Internet. Website downtime can, as I mentioned, bring about substantial losses of revenue, which is why these attacks have to be stopped at all costs.
Now, when it comes to the targets for these attacks, they are usually websites of some high-profile companies and businesses, as well as important government agencies. They target the websites that are hosted on major web hosting providers, ensuring that these pages stay down for a couple of hours.
If the problem is not dealt with, or is dealt with poorly, then the downtime can be prolonged indefinitely and can, after a while, cause the owner of the website (be it a business, a government agency or anything else) to break, usually financially.