lah3symzeo.com

Definitely malware or some sort of. Googling the URL throws up nothing but a link to this thread here.

In addition to running a complete scan*, as maria__ suggested: check if you have any strange browser plug-ins/add-ons installed and remove these.

* Download and install Malwarebytes and run a complete scan of your computer. If the program finds any malicious files, let it remove these.

Definitely not official Flash Player update notification.  Most likely malware, adware, etc.  I recommend running a complete scan on your system (virus, trojan, adware, malware, etc).