Users install these applications unintentionally, as developers often use software bundling for distribution of PUPs. Usually, it is an adware-type virus that can also be called a potentially unwanted program.
The Safari opening by itself issue can be caused by the suspicious program installed on the Mac computer. It is possible to encounter the issue on other operating system versions too, so there is no particular update that could be causing this intrusive Safari behavior. The Safari opening itself issue appears on various versions of Mac devices regardless of the particular OS version, among which are Yosemite and El Capitan. Even when you force quit the application, it reopens itself and does the same thing when you launch the device in the first place.
The problem seems to cause lots of frustration because Safari opens a new window every few minutes continuously. On various IT forums, users reported Safari browser opening by itself. To repair damaged system, you have to purchase the licensed version of Reimage Reimage.