[Update: After discussion with IE team, I revised my article as following.]
When visiting some AJAX extensive web sites, IE7 may cause temporary CPU spike.
I have discussed this with the IE and Anti-Phishing team and they are investigating this, but it does not impact all Ajax sites. The best workaround that helps provide protection against Phishing while helping you to customize performance on certain sites is as follows
1) You can add the affected sites to your trusted sites by going to Tools->Internet Options->Security->Trusted Sites, and click the “sites” button.
2) In addition, you may also need to disable Phishing filter for the trusted sites zone by going to the same trusted sites configuration page, click the “custom level…” button, scroll down to “Use Phishing Filter”, and select “Disable”, then restart the browser.