Prevent installation of malware, spyware... Admin password requirement I am new in Mac world. I am the only user of my Mac with OS X 10.9.3 but sometimes other people use my computer. 

My purpose is to prevent installation of malware, spyware and surveillance software.

Is OS X secure about this, if not, how can I make it secure? 

Can I let my Mac ask administrator password whenever a user including admin and Guest accounts install applications?
If other people use only the guest account, then they have no privileges to install anything.

I have added another account (beside the admin and guest account) which I use for daily work. The reason: sometimes someone ask me if he can use my computer for a short moment, and this way I do not have to switch to the guest account.

And because this third account has no admin privileges, it is more secure than using an admin account for daily work.