Some virus programs detect js/tiny_mce/plugins/paste/js/pasteword.js as Infected file, to solve this issue, open the file and replace this line (8 th line)

el.innerHTML = '<iframe id="iframe" src="javascript:\'\';" frameBorder="0" style="border: 1px solid gray"></iframe>';

With the following one:

el.innerHTML = '<' + 'iframe id="iframe" src="javascript:\'\';" frameBorder="0" style="border: 1px solid gray"></iframe>';