As I mentioned in this eWEEK story on the conspicuous absence of information on security-themed goodies in Internet Explorer 8, it looks like the browser refresh will have some form of malware protection.

This screenshot from Microsoft showing the new Safety Filter suggests there's a drive-by malware-blocking component:

From Microsoft's explanation:

The Safety Filter continues to block known Phishing sites and now blocks sites known to contain malicious software that could harm users' computer or steal their information.

It looks like IE 8 users will be able to use the Tools dropdown to turn on/off the Safety Filter or check Websites on the fly for potential dangers. Microsoft is now allowing IE users to report unsafe Web sites.

The existing Phishing Filter in IE 7 uses a client-side whitelist and a server-side blacklist to flag offending sites so it's a safe guess that this has been extended to include sites rigged with malicious executables.