Since so many of us use Adobe Acrobat or Adobe Reader, you should read this security bulletin from the National Cyber Alert System (http://www.us-cert.gov/).
National Cyber Alert System
Cyber Security Alert SA09-051A
Adobe Acrobat and Reader Vulnerability
Original release date: February 20, 2009 Last revised: --
Adobe Reader version 9 and earlier
Adobe Acrobat (Professional, 3D, and Standard) version 9 and earlier
Vulnerabilities in Adobe Reader and Acrobat may allow an attacker to take control of your computer. Adobe has released Security Bulletin APSB09-01, which describes this issue.
Disable the display of PDF documents in the web browser
Preventing PDF documents from opening inside a web browser will help mitigate this vulnerability.
To prevent PDF documents from automatically being opened in a web browser, do the following:
1. Open Adobe Acrobat Reader.
2. Open the Edit menu.
3. Choose the preferences option.
4. Choose the Internet section.
5. Un-check the "Display PDF in browser" check box.
Do not access PDF documents from untrusted sources
Do not open unfamiliar or unexpected PDF documents, particularly those hosted on web sites or delivered as email attachments. Please see Cyber Security Tip ST04-010.
In Security Bulletin APSB09-01, Adobe describes an issue that affects some versions of Adobe Reader and Acrobat. By convincing a user to visit a web site and opening a malicious PDF file in the user's browser, an attacker could execute code or cause a computer to crash. Note that web browsers may be configured to open PDF files automatically.
More technical information is available in US-CERT Technical
Cyber Security Alert TA09-051A.
Adobe Security Bulletin apsa09-01 - <http://www.adobe.com/support/security/advisories/apsa09-01.html>
Securing Your Web Browser - <http://www.us-cert.gov/reading_room/securing_browser/>
Vulnerability Note VU#905281 - <http://www.kb.cert.org/vuls/id/905281>