It has happened to almost everyone at some point: you're trying to load a Web page, but instead of the page smoothly popping up, it seems to be scrolling or jumping around at random. This is caused by a processing slowdown somewhere between your computer and your Internet connection.
Slow Internet connections are one cause of this problem. In this instance, your computer is processing your user input (keystrokes and mouse clicks that tell your computer what to do) faster than the Web is providing the information for the page at which you're trying to look. This can cause your computer to backlog your commands. Then your computer executes your click and scroll commands as the Web page loads. From the computer's perspective, it is executing your scroll and click commands as soon as the Web page has loaded to the point that it can, while from your perspective the Web page is jumping and scrolling randomly.
Slow Computer Speed
Jumping and scrolling can also be caused when your Internet speed is fine, but your computer is too slow to efficiently process what the Internet is sending it. In this case your commands are being backlogged until the computer has processed enough of the Web page to execute your command. Again, this gives the appearance of random Web page movement.
Spyware or Viruses
Although the core problem usually remains either a slow computer or a slow Internet connection, one possible cause of a slow computer is spyware that has installed itself on your hard drive. Spyware is a type of malicious code that can collect information about you and send it to whoever deployed it. Many people pick these bits of malicious code up while browsing the Web, and your connection (and sometimes overall computer speed) is slowed by the spyware collecting and sending information about you.
On a slower Internet connection, page jumping can result from components of a Web page loading at different speeds. On a fast connection the entire page will appear to load at once, but on a slow connection different parts of the page will load faster or slower, depending on how large the objects' source files are. Thus, if objects with smaller source files are located further down the page than objects with larger source files, the bottom of the page will load first, causing your browser to focus on it. Then, it will jump up when the top objects load afterward.