I just got rid of one yesterday Win32:MultiPlug-LV[PUP]

Took me about 5 hrs in the end.
I'd been unable to keep my definitions up to date due to very sparse internet connection. Meaning I could barely connect to internet for a month let alone download antivirus and malware updates.

PUP = Potentially Unwanted Program

They come in on other downloaded software.

They change the start pages of your browser.

They link your searches to poor reputation sites or even bad sites.

They also add add-ons to the browser. Worth always checking in your add-ons and extensions in your browser. I had some kooky adware stuff in extensions that I didn't put there. I also had some other thing I didn't get myself and ended up finding a youtube vid on how to get it off as it wouldn't uninstall from "uninstall programmes" area. Ended up having to do about 10 steps and then to Registry and got it off that way. ugh

They bring up ads on webpages and underlined words and make words on webpages bold or underlined.

They slow down your computer and make it very difficult to get from one page to another even to check on what it is that has infected you or even to get off the page at all.

Basically they slow you down so much your computer barely is functioning because you're constantly being bombarded with alerts and ads popping up and other pop up windows etc.

BAD news.

Check and double check everything that you may download.
Read the "terms" before you do anything.