No genuine security software is going to open a window like that one. (There is no reason whatsoever for imposing a time limit upon your decision).
It sounds like your computer has acquired some 'adware' which is trying to lead you towards paying for a 'solution' to a security problem which doesn't really exist. (i.e. no virus has been detected by the software producing that window. It's that actual software which you need to get rid of!).
If you've already got an anti-malware program (either built into a security suite such as Norton 2010 or a free-standing program such as Ad-Aware or Spybot Search & Destroy) run it now. With a bit of luck it will get rid of the 'nasty' which has found its way onto your PC. Otherwise download and run the free version of Malwarebytes' Anti-Malware:
http://www.malwarebytes.org/mbam.php
You should then find that you won't see any more false virus alerts.
Chris