Mac acting all strange (Safari zoomes out, can’t open AppStore, Finder windows pop up)

Hi folks,

My iMac 27” late 2014 is acting quite strange since today.

Recently I have noticed that browsing the internet is kind of laggy - it gets stuck during surfing, YouTube videos buffer from time to time, etc.

Today, it went crazy.

I have opened up a site on both Safari and Chrome and the view zoomed out to 25%; pressing Cmd+0 did not help.

I wanted to reboot, but when selecting the option in the menu, the mouse cursor would go up and down, making it quite hard to click the restart button.

After restart, I clicked the Safari icon on the dock, but instead the Applications folder opened up, where I could open Safari from there.

I then surfed the web again, but again zoom to 25% and every single link I clicked on was opened in a new tab. So I looked for a forum to ask for some help - but could not type anything into the post window - I am typing this from my iPhone.

So, I looked for an update on the AppStore - just to find out that I cannot click the updates button there (but at least Mafia 2 is now on the AppStore!)

I am currently running a Bitdefender Scan to see if anything can be found.

Is there any advice you guys could give me or a hint what to do? Any help is appreciated.