As with all important laws, the Digital Millennium Copyright Act (DMCA) does many things. Overall, the point of the act is to prevent internet piracy. The law has in many ways been ineffective as it continues to be very easy to obtain pirated material on the internet.
As the internet has become more and more popular, and since internet bandwidth has increased, it has become increasingly common for people to distribute copyrighted material across the internet without permission. The first very popular way to do this was through the original Napster peer-to-peer filesharing application. The DMCA was meant and has been used to prevent this sort of sharing.
The DMCA also has provisions that are more controversial. Mainly, the DMCA allows creators of content like DVDs to sell those DVDs with digital rights management technology that prevents the DVDs from being copied. This is controversial since it can be seen as an infringement of a buyer’s right to make copies for their own private use.
Although the DMCA has helped to reduce piracy by, for example, being used to destroy Napster, it has not succeeded in ending internet piracy.