MacBook is acting strangely...

Recently, my mac has been acting weirdly. For example, from time to time it freezes the screen and I have to force shutdown it. Also, it even renamed two of my folders to 'Q' and 'QQQQQ'... I'm really confused. I'm thinking it might be a hacker/virus so I changed my netgear password, but I don't know it that will help. Does anyone know whats happening to my mac?