Keep getting messages that I Flash Player is out of date...

About a year ago, there was a widespread (and widely publicized) vulnerability in commodity wifi routers that allowed attackers to inject malicious code into the device's memory.  Since Flash Player is ubiquitous, it's the go-to product to impersonate if you're trying to get someone to install your malware.

If this is popping up all over the place (i.e. on legitimate sites) and you haven't update the firmware on your wifi router lately (or like most normal people, ever), there's a decent chance that it's infected.  The good news is that the infection is typically only resident in volatile memory.  Simply powering the router off and back on will resolve it (at least until something on the Internet re-infects it).

Once you've power-cycled your router, log in to it and install the latest available firmware.  That should prevent the problem from coming back.

If your router offers an auto-update option, definitely enable that (most older ones don't).  If not, it would be wise to set a calendar reminder for yourself to just check to make sure you're running the latest firmware every couple months.  If that sounds like a hassle, you might consider upgrading to one of the modern routers that *does* have automatic updates.

If the problem persists, you might consider whether the sites you're visiting truly are reputable, and/or running a scan from a reputable antivirus/antimalware vendor.

don't go to that site