As you download files from the Internet, your browser stores information about all files you downloaded. Download history stored by your browser can seriously compromise your security and privacy, as anyone who has access to your computer can see what files you have downloaded.
To protect your privacy and also to free memory and empty hard disk space you should clear download history. (See also Clear All History).
Select Browser History.
In Internet Explorer, select Delete Browsing history.
In Firefox and Google Chrome, select Clear Browsing history.
In Safari, select Delete Browser history.
In Opera, select Clear Browser history.
Open the Tools menu.
Select Delete Browsing History or press Ctrl+Shift+Delete and select Download history.
Click the ‘Delete’ button.
To delete download history automatically, select Internet Options and check Delete browsing history on exit.
Open the Tools menu and select History.
Select Clear Recent History, open Details and select Browsing and Download history.
Click Clear Now.
Select Tools, then check Clear Browsing history and click Delete All.
in Google Chrome automatically
Select Tools, then check Clear Browsing history automatically and click OK.
Click on the ones you want to remove or clear all.
In Safari Automatically
Click on Edit then Preferences.
Go to General tab.
In the section Remove download list items choose and select “When Safari quits” or “Upon Succesful Download”.
Go to Menu.
Remove items individually or select clear all.
To delete all the download log of your MAC type:
sqlite3 ~/Library/Preferences/com.apple.LaunchServices.QuarantineEventsV* ‘delete from LSQuarantineEvent’