You can read about it HERE and HERE.
You can directly download the Adobe Reader 10.0.3 update HERE.
You can directly download the Adobe Acrobat X 10.0.3 update HERE.
The security flaws involved are those Adobe posted on April 11th in the second article linked above. These are the promised updates of Reader and Acrobat, ahead of schedule by four days. Thank you Adobe!
Computer PWNing through the use of PDFs and Flash media is thick and fast these days, particularly on Windows, including Windows 7 (7ista). I have read speculation that hackers have a pile of 'zero-day' Adobe security hole hacks that are being used one after the other as Adobe provide patch after patch, trying to keep up. Note that it is possible to at least compromise a Mac using similar cracking methods and Trojan horses.
THEREFORE, user beware. I wrote in detail about precautions and protections available if you must use PDFs and/or Flash. Simply scroll back through my previous blog posts.