Why are there viruses even in a DVD/CD disc?

Last week I downloaded many softwares from the internet, and scanned all together which had no viruses or spywares,..then burned to a DVD disc for a backup master copy...but today when I tried to use those softwares from the disc some softwares were found infected with viruses...

it was OK last week, but today with many viruses...and I know my PC is safe from viruses after scanning twice, except in the disc...why are there viruses even in a disc?

Why are there viruses even in a DVD/CD disc?virus protection software

I can only give you a scenario on which a virus works......Virus are programs which can not execute itself automatically...until it is not fiddled or executed......in your case.....it seems that it was not effective on those files (.exe files) until it was fiddled by your Antivirus program....once those files where checked by your Antivirus....the virus in the Memory (as in process memory) effected those files......also as you told me that it is now detecting those virus.......

On other scenario; as you told me that you downloaded the files from Internet and then scanned at that time......found no viruses......now your Antivirus was updated automatically and new virus definations where provided to your antivirus program....and now today when you ran the scan again the viruses which where undetected by your antivirus last time was detected after updation...............it is not that your file was infected at that time...it was....however it was not detected......I believe that I made it clear for you.......Hope I did.... ;) ......