Apparently this happens to me out of nowhere for Illustrator, Indesign and Photoshop as well. I have the latest version of the software.
Whenever I open, for example in this case, a Illustrator file, and whenever I try to use any kind of tool, for example the selection tools with V and A, illustrator changes to the eraser tool and erases everything once i hold the mouse button. If I hold command or sometimes shift, the icon changes from eraser to the appropriate tool, but still while holding that button and the mouse button, it still erases things. Changing workspaces and resetting workspaces worked previously but now nothing happens no matter what I do. I think I have hit every key on the keyboard to see if I did something wrong. I am out of ideas. Anyone?
I am in a tight spot because I need to layer around 200 paths, compounds and groups for a upcoming animation and selecting everything with the selection tool is much easier then to check every single path and compound to see its contents and drag it into a layer... (the original artwork was made for online, never for animation so it was never layered, thats my job i guess)