Attackers are exploiting an Internet Explorer flaw ahead of a planned Tuesday fix for the vulnerability, according to the Microsoft Security Response Center. "We're looking into limited, targeted attacks on a known Internet Explorer issue we're addressing in tomorrow's bulletins," read a Monday tweet. Microsoft is readying 17 patches to address 64 vulnerabilities in its April security update, including publicly known issues in in the MHTML (MIME Encapsulation of Aggregate HTML) protocol handler and Windows Server Message Block.