How to know a downloaded file is safe or not?

[Kakero]

I've got a few questions..

1. Is there any way to know the file that you have downloaded from a site is safe from any virus or backdoor program ie keylogger?

2. Before you actually download a file, is there any way to know that the link that you are about to press in order to download a file is safe or not?

I think I have more question about this but I can't remember what they are. ( it's midnight already )

thanks..

[Vaskez]

1. Virus scan it and run spyware ad-aware on it - I'm sure you've heard this advice 50 times already so why bother asking?

2. Not technologically, since a link is just a Uniform Resource Locator reference that your browser uses to FIND the file and nothing more. However, using common sense, you can evaluate whether it is likely to be safe or not. Files from domains of large companies like MS, IBM, Amazon etc. are very likely to be safe as they have reputations to uphold. Files from hacker or warez sites are most likely to be unsafe. Files from small personal sites are in the middle in the safety rankings.

[Bungleau]

Like Vaskez said, you can tell your virus scanner to scan that particular file, even if it's still zipped or in an exe. Of course, part of the issue is knowing where you're downloading from to begin with...

From the URL perspective, one thing you can check for is what the actual URL is. Look for any extra HTTPs in the middle; they can signify that someone is trying to hide the real URL so you won't notice it. For example:

http://www.microsoft.com@http://www.gotyousucker.com

looks like Microsoft, but it's really gotyousucker.

If there are extra https, make sure you're comfortable with the real one.

[Intrepid]

Just keep your virus definitions up to date, try to be reasonably confident that the file you are downloading is what it says it is, and keep in mind that some executable files (.exe .scr .com etc.) can all contain viruses and can execute without you clicking on them.
I have about 1 week untill i can get my new computer working and will install onto a 120 gig harddrive, untill then i am stuck with my 6 gig and i am too lazy to protect it properly, i have no virus protection, no adaware, no firewall, and i use kazaa, i am confident that it has viruses on it, although it has been a while since i scanned.
My point is virus protection helps, not all viruses are destructive, and the best advice i can give you is to backup.

[Kakero]

okay, so the only way to know the file is safe or not is to download it and the nscan it using anti virus program. But what about backdoor program like keylogger ? can antivirus program pick it up? or are they considered virus as well?

[shamrock_uk]

Another good way to protect yourself against things like that (in addition to what's already mentioned) is to run an application protection program. I use BlackIce, it's a lousy firewall so i have that part disabled, but it will also pop up a confirmation box when any program executes giving me the option to run or terminate. It keeps a baseline, so you'll only have to add things once, and it has saved me twice from programs that tried to execute and that my virus checker did not pick up.

Your other stop is a good firewall - if someone is logging your keystrokes there will need to be an outgoing connection at some point from that program in order to impart the information. Use a learning firewall that blocks all traffic and allows you to add by application - that way you have complete control over what applications send information in and out. I use Kerio which i find to be great, i believe ZoneAlarm is free and also supposed to be good.

www.winfiles.com is bound to have some alternatives to the ones i've listed

EDIT - and to answer your last question, a key logger isn't classed as a virus,but most decent virus scanners will routinely scan for backdoor exploits like trojan horses that aren't viruses, so you may well find that a few common key loggers are included in the scan.

[ 02-16-2004, 10:38 PM: Message edited by: shamrock_uk ]