I am new to this forum and also a newbie to software stuff. Recently while checking my emails I noticed some website opening in new tabs which were full of adult content. I start panicking when my kids use the pc but fortunately they are too young to use the internet but I am worried if by mistake any of the windows pop up. I am not sure whether it is a virus or some thing else. I don’t have any antivirus software installed on my computer and now I am bound to look for one.
Also while searching on the net I came across two software : Internet security Buy Norton Internet Security 2009 (14125794) :: eCostSoftware.com - UK Software Supplier and antivirus software Buy Norton Antivirus 2009 (1 User/3 PCs) (14172242) :: eCostSoftware.com - UK Software Supplier Is there any difference between the two? Which one should I opt for? Is there any difference between the two?

There are two ways that you can opt for in using anti spyware/malware/virus protection.
1) free ware which is usually single programs that you can download and use for free
2)pay for...which are usually a suite of programs that auto protect your system..

The difference is that the suite comes in one package and the free stuff is multiple applications from different sources that work together to protect your system...The paid for suites usually self update while the free stuff usually have to manually update(some are self updating)
The other thing is that the suite packages are also quite demanding and are prone to trying to rule your computer.

What you are describing is not a virus (but could be) but more malware than anything else.

Google for this and download it and install it and see if it cleans out your problems.

superantispyware free version or trial

antimalwarebytes free version or trial.

The two norton suite packages are both the same thing except one is for single computer and the other can be installed on three different computers.
Personally, I don't care for Norton/symanyec ., but for unexperienced computer users they would be the best till you learn the ins and outs of surfing and downloading properly.

Also, being a freeware user to the max (openoffice, linux, you name it...) I would personally NOT recommend Norton (or many others by symantech) but also some alternatives you could try. each are very good and are:

AVG free 8
Pc tools anti virus free edition

NOTE: spywareblaster very handy too. just type them into google and find a download mirror