WordPress Virus

Good Day All,

My website seems to have a virus. I keep getting the following errors:

Media Type: text/plain
Virus Name: MGW: Heuristic.BehavesLike.JS.Infected.A

Is anyone familiar with this?

When I run a virus scan it says that 20+ files are infected but does not tell me how or where exactly int he file.

I have two questions:

1) How do I fix this? Can someone walk me through it please???
2) What antivirus plugins should I install to prevent this in future?