While your victim is away from his computer, change all of his browser bookmarks so they go to adult sites or shock sites. Be sure to keep the title the same though, this way he or she won't know its changed until they click on it!
While your victim is away from his or her computer, change the settings of the mouse. To do this, just go to to your control panel and then mouse properties. You could swap the functions of the buttons over or make the mouse move faster or double click faster etc. Whatever you change, it will be sure to leave your victim confused for a long time!
Very Slow Mouse
Another funny computer prank you can pull off on your friends is by slowing down the mouse pointer. You will have go to the mouse properties in the control panel. Adjust the pointer speed settings to make it as slow as possible. Leave it for your victim to start using the mouse. They will be confused and irritated at the same time, when it will take ages just to move the mouse across the screen! It will take them ages to figure out what is the reason for the slow mouse!
This is a great computer prank for you to pull on your colleagues and friends. While your victim is not a their computer for a lunch break, take a screen shot of their desktop as it is, by pressing the 'print screen' button. Ensure that you hide the mouse cursor outside the frame in one of the bottom corners. Next, paste the screenshot in Microsoft Paint. Then, on their desktop, hide all the icons and the taskbar. Simply Finally, set the screenshot you have saved as the new desktop background. And the prank is done! Your victim won't understand whats going on when they are unable to do anything on their desktop even though everything appears normal!
A lot of office work requires typing and this gives you a great opportunity to play an office prank by changing certain settings in Microsoft Word. A great office computer prank you can play is to change certain 'autocorrect' options. All you have to do is get onto your victims computer when they leave it and open word. Then go to the 'autocorrect' options and replace commonly used words with funny ones, like 'and' with 'boo boo' or 'the' with 'pops'.
A classic office computer prank is to simply turn down contrast on the screen to the minimum, and adjust the brightness to the maximum when your colleague is not around. This will make the screen appear blank. This should definitely drive the victim mad as they will not know what is wrong with their computer. Checking for contrast and brightness settings is the last option they will think of, and instead call for someone to repair the monitor!