How do I delete "__MACOSX"?

Drag it to the Trash, open Trash and go to Finder > Secure Empty Trash

Try to google " __macosx folder in zip" without quotes.

There are enough information available there.

Best.

Where do you have this folder? I recommend you to boot into single user mode, but it's a bit dangerous, so I need to know where you have the folder

Move it to Desktop. First, do a back up of your files. Then, reboot your Mac into single user mode (Command and S buttons during boot). You will be a root user, so do this:

cd /

cd /Users/(user)/Desktop

sudo rm -rf __MACOSX

sudo reboot

Replace (user) with your user's account name

Whoa! That's a pretty bad set of commands! There's absolutely no need for "cd /" or "sudo reboot". For that matter, "sudo reboot" really doesn't make much sense... it doesn't take root priviliges to reboot, and if rebooting were actually necessary, it would be better to just choose Apple -> Restart. And I'm not sure why you think it's necessary to move the folder to the desktop before doing any of that.

Yes, they are, but it looks very bad to delete the folder.

Since you're seeing obviously nonsensical progress info when secure emptying the trash, I would be concerned you may have a corrupt hard drive. Try restarting in recovery mode (hold down command-R at startup). Once there, select the Disk Utility option, and repair the hard drive. If there are any problems that can't be repaired, you'll need to bring out the bigger guns... try something like DiskWarrior.

If the disk checks out okay, let's just nuke your trash folder entirely. This is dangerous stuff, so be sure that you copy these commands verbatim and paste them into the Terminal. Don't try to re-type them in the Terminal. A single typo could cause you to erase the entire hard drive. And it should go without saying that you need to have a good set of backups before doing anything like this.

All that said, here goes... cross your fingers and toes! Paste the following command into the Terminal:

sudo rm -rf ~/.Trash

Enter your password at the prompt, and don't be surprised that it doesn't show anything when you type. Then wait until you get a new $ prompt. Once that happens, quit the Terminal and log out of your account, then log back in. (Or restart the computer.)

Let me know if none of that works.

I decided to try them in order, and found that mende1's solution worked.

It worked, but it was more awkward than it needed to be and revealed a lack of familiarity with Unix that is concerning in conjunction with one of the most dangerous commands you'll ever use (sudo rm). I say this not to insult mende1 - who was, after all, just trying to help - but as a warning about the dangers of using Terminal commands. Many people giving out such tips may just be copying them from elsewhere without fully understanding them, and may not get it quite right. As I mentioned earlier, a very small error in a sudo rm command can erase your entire hard drive. I've seen it happen.