If you have discovered that the software you downloaded as an Internet browser plugin is indeed malicious, then it is best to do all you can to get rid of it. If you are familiar with computers, you can buy a anti-malware program to clean up the software from your hard drive. Depending on how bad the software might be, the cleanup may require more than one anti-virus software application. If you are comfortable around a computer, you may attempt the virus cleanup yourself. Someone who is unsure of what they are doing should take their computer in to a certified repair store. If your computer is still under warranty, you may be able to have the computer cleaned for free or at a reduced price.
If you do decide to have a go at cleaning the computer yourself, this can be quite intense depending on how badly your computer has been infected. One of the first steps will be to try and backup any of your documents or important files that are saved on your computer. This might not be possible if you are unable to access your hard drive. If you can access your hard drive, then try to avoid backing up any files that are applications or .exe as these are more likely to have been infected. Then you can run the anti-virus program and have it remove any malicious files that are detected on your computer. Depending on the program you used as an anti-virus, it can instruct you to backup your hard drive before it undergoes the cleaning process.