Download shortcuts: Windows XP, Windows Vista/7 32-bit, Windows Vista/7 64-bit.
Instead of relying on a virus database for detections, MSE 2.0 has a heuristic engine that can detect previously undocumented malware, so you're safer against new variants. It's worth noting that this is often a double-edged sword, as heuristic technologies can also increase the likelihood of false positives.
MSE 2.0's network inspection feature is as straightforward as it sounds: it watches for suspicious traffic and protects your system from network-based attacks. Unfortunately, this isn't available for Windows XP users as it requires the Windows Filtering Platform in Windows Vista and Windows 7.
Microsoft has also improved the way MSE works with other Windows software. The application is better at protecting IE users from Web-based exploits such malicious scripts. Additionally, the MSE installer prompts users to enable the Windows Firewall, which can now be configured from within the antivirus.
MSE is arguably the best free antivirus available for Windows and it remains free for both home users and small businesses with 10 computers or less. Enterprises can look forward to the new Forefront suite, which utilizes the same engine is MSE and should be available for volume licensing customers in January.