where can I download Mac OS X Yosemite 10.10.5? My system seems was attacked by some kind malware.

You can download OSX 10.10 from the app store, you would then need to upgrade it to 10.10.5 again also via the app store. Also see How to reinstall OS X on your Mac - Apple Support

Or you can use Recovery (hold down alt on start up and select recovery if your computer supports it). But what do you mean with my system seems was attacked by some kind malware? Do you believe you have a malicious program or something? Could you provide more details?

Cheerio~

I'm afraid that OS X Yosemite is no longer available in the app store. You can download OS X Capitan instead. Alternatively, you can hold down Command + R keys during boot to use Recovery mode to restore a backup or do a clean install of your current OS X (which in this case would be OS X Yosemite). This will require an internet connection. Hope this helps and good luck.

Don, you can download Yosemite at

OS X Yosemite 10.10.5 Combo Update

or

OS X Yosemite 10.10.5 Update

Howard

1. In the Appstore in the Purchased tab is Yosemite (latest version) available for download.You do not have to re install.

2. The message on your screen is a SCAM, do not react at all. Quit Safari from the menu, then restart Safari while holding the Shift key, then in Safari open the Safari menu and do "Clear history and website data". That is all.

To feel even more safe, download AdwareMedic (now called malwarebites) from http://www.adwaremedic.com/index.php and run it. That will remove all adware from your mac.

That is all.

Lex

I would recommend that you disable a default setting in Safari. Remove the checkmark in the checkbox beside 'Open "safe" files after downloading.'

Additionally, I would recommend that you install the Safari AdBlock extension.

Select the "Extensions" tab then click on "Get Extensions" to search for it.

Follow the on screen instructions to install it.

Glad to hear you solved your problem!