When a user uses overwhelming amount of data, it puts a burden on the entire network and can actually slow down neighboring connections. It can also signal serious problems that negatively impact not just your Internet connection but your computer as well.
You have a virus (or even viruses): When we notice that a customer is suddenly using way more data than they normally do, it’s often an indication that the customer has been infected with a nasty virus. Many viruses receive and transmit data and thus can cause a huge increase in the amount of information used.
Someone else is stealing your Internet connection: An unsecured wireless network leaves your Internet connection open to use by anyone close enough to pick up the signal. When your neighbor, who doesn’t pay for the Internet, leeches off of your system, it can slow your speeds and also increases your data consumption. Expected data usage is based off of the number of customers in an area. Each non-customer who “steals” a connection makes it harder to ensure that data is flowing well for everyone
Keep an eye on your backup plan: Online backup is a great idea! However, since these sites upload your data each day, your usage can easily add up. This is especially true if you have data heavy files such as graphics programs or movies or if you are uploading your files for the first time.