ZDNet's security blog points to an update to Google's malware warnings. Like McAfee SiteAdvisor, now each web site has a special diagnostic page that lists answers to four questions:
1. What is the current listing status?
2. What happened when Google visited this site?
3. Has this site acted as an intermediary resulting in further distribution of malware?
4. Has this site hosted malware?
Here's, for example, the diagnostic page for google.com: http://www.google.com/safebrowsing/diagnostic?site=google.com, which lists some interesting facts.
"Of the 274621 pages we tested on the site over the past 90 days, 4 page(s) resulted in malicious software being downloaded and installed without user consent. The last time Google visited this site was on 05/22/2008, and the last time suspicious content was found on this site was on 03/13/2008. Malicious software includes 4 scripting exploit(s), 4 trojan(s). Successful infection resulted in an average of 10 new processes on the target machine. Malicious software is hosted on 4 domain(s), including 126.96.36.199, truemaybe.com, abc-powers.com. 5 domain(s) appear to be functioning as intermediaries for distributing malware to visitors of this site, including xtraff.biz, x-traffic.ws, smartvideochannel.com."
Despite all of these findings, google.com is not listed as suspicious, probably because the domain is whitelisted or the suspicious content is not very significant. It's likely that the domains listed above are from Google's search results, so that means the anti-malware system doesn't respect robots.txt.