This is interesting:
"It turned out that by combing through the access logs for static.php.net it was periodically serving up userprefs.js with the wrong content length and then reverting back to the right size after a few minutes. This is due to an rsync cron job. So the file was being modified locally and reverted. Google's crawler caught one of these small windows where the wrong file was being served, but of course, when we looked at it manually it looked fine. So more confusion." [emphasis added]
If you spend some time surfing the net reading comments about this incident you'll commentary criticizing Google, disbelieving the alert etc, and even a person or two recommending that such alert services be turned off! I also find the way that information is presented by the Safe Browsing webpage to be confusing, as I think a lot of us may do (I wish Google would redesign/recompose the way they present the information) but I would never recommend that such services be turned off.