The short of it is that since you're reading this on a computer go and do your system's update.
Windows almost always has updates.
Mac OSX has one for Safari for the supported operating systems.
Even my Linux system needed it, but that's normal when you have 1500 projects updated by probably as many different groups of people.
What got me started on this was that this morning before sunrise when I started the main computer, I saw a "helpful" yellow text show up on Windows. It was warning me that there was an important update available.
I've gotten so that Windows seems to be the Boy That Cries Wolf, but ok let's check. Definition Update for Windows Defender. It's a built in virus scanner in Windows 8 and above. It's the love-child of the old Microsoft Security Essentials. I've used it for quite a few years now, and while I trust it, I have grown to expect a message telling me to update.
Since it is Windows, it is the operating system everyone seems to like to attack. More ways than one, I'm afraid.
I installed that particular update, and since it didn't demand a restart of the system, I shrugged and got on with my business.
I also have a Linux machine, two actual laptops, and a number of virtual machines, so just for giggles, I thought I'd check. 172 updates on Linux, but that's not a shock. With Linux, avoiding viruses is easy, just go to a known repository and use their software - in Windows terms, only use Windows Update and don't install from an unknown source.
That doesn't help with backdoors, and that is what the Heartbleed bug was last month. Someone had found a backdoor into the software and everyone needed to change passwords.
You did change your password didn't you?
It went on its happy way, and I realized that I had a couple other virtual machines that needed attention. Since they're all lightly used, they'll get it when I run them. Virtual Web Servers and the like.
Even Apple has gotten in the mix of it all, since they want an update to their browser. Part of being popular I guess, and that means that iPhones will probably need it too.
I know for a fact that my Android phone needs an update, but that's a very different thing. It's a very old version of Android that's named Gingerbread, on a very old phone, relatively speaking. Even the "alternate ROMs" don't support this phone fully. Not to mention the software that I installed through Google Play needs updates. Since I don't actually want Facebook on my phone, I tend to ignore things like that.
So if you got this far, go find out how to update your Windows Computer (Start, Windows Update), Apple Computer (Apple Menu) and Linux Computer (Software Update or Synaptic or "apt-get update") and watch the pretty thermometers go.
Now, if you will excuse me, my Linux Virtual Computer says Restart is Required. Strange that Windows didn't need it, but Linux did... Never mind that, time to restart!