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I would be grateful if anyone with a bit more knowledge on viruses could answer the following questions: 1) If I download a file(piece of software) which contains a virus, am I correct in assuming, it will not attack(harm) my system until I try and install or open it? 2) Is it possible for a file/piece of software containing a virus in a non detectable form to be downloaded and scanned with an antivirus program that does not pick up the virus, only for it to become active once the file is launched? 3)What is the safest way to download a suspect file, to avoid contamination of your computer (download to a memory stick and scan it there??) Any comments would be greatly appreciated.
1) By downloading, you have installed any virus's. Opening (especially if its in attachment form) will activate.
2) It is possible, and there are programs out there that will dig deeper for 'root' problems.
3) If you suspect that there is a virus, then the safest way is not to download.
If you have a anti-virus program on your machine, then always make sure that its up to date.
To get really into this subject, then a Google search should bring up some convincing answers to any questions you are seeking.
There are so many variants of virus/malware and the way they behave, that it is impossible to have a foolproof way of detecting one in a downloaded file.
A workaround is to take a full backup image of your harddrive using a program like Acronis, and store that on a separate external harddrive that can be detached. Then download and do what you will with the suspect file. If it messes all pc up etc. you can then wipe your C: and restore it with the backup image and all will be as it was before you downloaded the dodgy file.
A variant of that is to have a separate cloned hd that you can play with and then take out and put your original hd back in to be 'as before'
Thanks a lot for the info guys, appreciated
1) Downloading a file does not, in the normal course of events, install it. But if you were, for example, to "run" an installer from within your browser the download is immediately installed (as it is downloaded). Also a virus that is crafted to exploit a "hole" in the software that is doing the downloading, could cause itself to be installed via such a hole during the download - that is one of the reasons why one should keep one's software (esp. Windows and Browser) up to date.
2)Yes. Quite simply no AV program is guaranteed to pick up every possible virus, so the scenario that you have described is clearly possible.
3) The short answer is that if you really suspect the file, don't download it. If you must download it, as mentioned before - make sure all your system is fully up to date first (so all known and fixed holes have been plugged). Doing an image as lotvic suggests is not a bad idea. I would also recommend that after you download such a file, submit it to one (or more) of the online scanning services that will scan it with many AV programs. See:
Thanks Batch, great help
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