Computer viruses are the most common causes of slow Internet traffic. Most viruses infect computers through infected emails or through external portable hardware shared between multiple computers such as flash drives. Viruses divert the computer's resources, including Internet services, therefore causing a slow connection when running other programs through the same connection. To overcome this nuisance, install virus protection software on computers to prevent and remove any infections.
Internet traffic can also become slow due to a bad network adapter installed in a computer. Such cards are notorious for slowing down Internet connection --- not only for the host PC but an entire group of computers if connected through a local area network. Bad network cards cause traffic by sending useless data through the Internet connection. Nevertheless, you can easily solve this problem by replacing or disabling the bad adapter.
Spyware and adware are types of advertising software that come attached to other products. This software can use up some of the computer's resources and sometimes the Internet connection as well, therefore increasing Internet traffic. Fortunately, installing anti-spyware software can prevent any spyware or adware from causing any inconveniences.
Internet service providers (ISPs) supply PCs with Internet connection ---usually at a cost. PCs connect to routers that relay data to the ISP, which in turn transfers it to the larger World Wide Web. At times, the router may become congested because too many PCs are connected to it, greatly reducing the rate of traffic flow through the Internet. On the other hand, ISP servers may also become congested due to too many subscribers causing too much data flow through them, in turn causing congested Internet traffic. Reducing the number of PCs connected to a router would solve such router-related problems, while expansion of ISP resources reduces server-related problems.