Why Do Zipped Files Get Corrupted On Download

[Harry]

I recently downloaded a zipped file and then tried to unzip it with its self-extractor. In the middle of unzipping it gave me a CRC file error and would not continue.

Fortunately I had a nice little program called Advanced Zip Repair which fixed it. But I don't understand why it is that zipped files get corrupted like that. I thought zipped files were supposed to protect files from getting corrupted.

[reboot]

It may not actually be corrupted, and can depend on which program was used to zip it.
If I use Winrar to make a zip, winzip claims it's corrupted, but winrar works.

[David_Jones]

Shouldn't happen with a file that is a self extracting zip though?

David.

[reboot]

Yup. Use Winrar to make it, and it'll give you the same message/problem.

[David_Jones]

Bizarre - Obviously has to be a bug in Winrar if its self-extracting files are corrupt.

Can't you change to something else than Winrar?

David.

[reboot]

Winrar offers far better compression than winzip (and it's clones), which is why many prefer to use it. It's not a bug, it's by design.
For personal use, I always make .rar files, especially nice for creating smaller chunks from one big file, and they join together automatically.
If you're going to be downloading stuff from those places, then get a copy of Winrar and use it instead of Winzip.
If you're on XP, just use the built in zip functions, which will coexist with Winrar with no problems.

[morriswindgate]

And the newest version of WinRAR will extract ISOs

[David_Jones]

Useful to know.

I'll have to try WinRar.

It still seems to me it must be buggy though. If I create a self extracting zip with WinRar and it won't then extract, how can that not be a bug?

I could entirely understand that Winzip (say) won't be able to read the self extracting exe, but I would only send a self extracting file to someone who doesn't have winzip or winrar wouldn't I?

Yours in slight confusion,

David.

[reboot]

Something about the way it makes the self extractor. Seems it only works on other system's that have winrar installed.
I know there's a ton of complaints about that on various BBS's, but the author insists that it's designed that way, mostly for the hacker crowd that first started using winrar, so that the lamers couldn't steal their archived files easily. You had to be "in the know" to use it.

That said, there are any number of reasons that a downloaded file won't extract properly, I was just trying to point out that the most common cause that I've found, is because of the use of winrar.

[David_Jones]

Thanks for the enlightenment!

[imbest123]

it could be that you never downloaded it completely

[reboot]

OK, here's another couple of things.
If the file upload was interrupted, and then resumed originally, it may be corrupted, because it didn't resume properly.
Same problem with a download, especially using some of the not-so-good download managers.
If the file contained a virus or trojan, the virus scanner used on it originally may have rendered it useless, and the unzip program can't decipher the problem, or checksum's don't match.
If the file contains a virus or trojan, it may be "corrupted" by YOUR antivirus scanner upon download, as the AV tries to keep the file intact, while removing the trojan bits.

[Dreamscape]

Check yourself for the CIH virus

Having it happen with all self extracting files would make me wary. It is an old, easy to remove virus, so do not fret. But hopefully and probably this is not the problem.