Windows Vista users (and IT folks taking care of Server 2008 computers) should watch out for a new security hole involving Windows file sharing. A remote attacker could assume full control of a vulnerable computer by exploiting a flaw in the SMB protocol for Windows file and printer sharing.
Most home users should already have a firewall in place that blocks attempts to reach the ports that SMB uses (139 and 445). Microsoft may have a patch available by the time you read this, but as of this writing no fix was yet available. For more details, see Microsoft's security advisory.
In a recent Microsoft monthly release, the ActiveX patch-up continued with an additional fix for the buggy Microsoft Active Template Library (ATL), along with updates for Windows Media Player and other software created with ATL. It's a critical fix for Windows 2000 SP4, Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008, according to the MS09-037 bulletin.
Another patch closes holes in the way that Windows 2000, Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008 all handle AVI video files. Opening a specially crafted, poisoned AVI file could allow an attacker to run any command on your PC, but the MS09-038 patch shuts the door.
Browsers Bump Up
You'll also want to make sure your browser of choice is up-to-date as well. New versions of Firefox, Chrome, and Safari all came out in the past month or so.
Viewing a tainted image or site could trigger an attack for Safari users who haven't picked up the latest patch for both Windows and Mac. Vulnerabilities involving the CoreGraphics and ImageIO components affect only Windows, but problems in the WebKit browser core affect Macs as well, as does a flaw that could promote a malicious site in the Top Sites page. Run the Apple Software Update tool to confirm that you have Safari 4.0.3 or later.
Security Updates for Macs
Mac OS X 10.5.8 fixes a wide range of vulnerabilities, including some that could hand control to an attacker if you view a poisoned image or Web site crafted with malicious XML. While Mac users are still immune to the vast majority of Windows-centric malware, Mac-specific threats are now appearing, as evidenced by Apple's inclusion of malware scans in Mac OS X Snow Leopard that will attempt to block two known Mac Trojan horses. Run Software Update from the Apple menu to pick up the new OS X, and see Apple's support site for full details.
Speaking of Snow Leopard, the new OS installs an old, unsafe version of Adobe's Flash, even if you had a new, fixed version of Flash before upgrading. Check your current version at Adobe's Flash version test page, and if necessary nab the latest version.