i thougth about using linux for some time now too, but then i thought, well what do i need my PC for, and came to the conclution that its not really worth it to change to linux and learn how it works(all that command line stuff etc).
i usually use my PC to surf the internet (ok for that i would me reasonable).
to play games linux is of no use, to watch movies and stuff on the tv via my ati card linux again is of no use unless u really know what u are doing or can program some script etc for yourself.
and to do some film editing or converting i dont need linux as well.
so in the end windows is the more reasonable choice for me(and hey i paid for it, so i'm gonna use it until its not supported anymore

)
Edit: and for that security issues, i never had problems with them, althoguh i have no antivirus installed,
and lately there have been some security issues with linux as well, i think there are as many problems as in windows but since there are not so many users they are not found so fast on one side, and on the other linux users are mostly freaks who know what they are doin and know how to make a PC save.