I have some malware on my computer at work that I'm having a hard time getting rid of. I'm only interning there over the summer, so I'm guessing that it was downloaded by the previous user because I noticed it as soon as I opened my web browser for the first time. Whenever I'm using a web browser (this occurs on all web browsers that I've used including IE, Firefox, and Chrome), the same ad appears on every website I go to (even on sites where there should not be ads). This ad obstructs either the bottom left or bottom right portion of every page I visit and also installs unwanted cookies. I ended up using adblock to manually block out the ads; however, what troubles me more is that every once in a while when I click on a link I get redirected to a website I never intended to go to. It's quite frustrating when I'm trying to get to an important page and instead I end up at an auto glass website or some advertisement saying I've won a prize.
I have tried remove the adware using multiple antivirus softwares including Windows Defender and Malwarebytes, but none of them seem to be spotting the the virus. Is there something I can do to remove this? I've put up with it for a few weeks now, and it's gotten very frustrating.