According to a recent Wired article, Microsoft Security Essentials recently identifying Google Chrome Browser as a Trojan. This issue has been identified by both Microsoft and Google, and they are working on an update.
Microsoft’s Security Essentials anti-malware tool has mistakenly identified Google Chrome as a password-pilfering Trojan — and actually removed the browser from many users’ machines — but a fix for this rather amusing false positive is now available.Here is the Wired article...
UPDATE 3/15/2012: This has since been repaired. Typically events like this are not uncommon; security software removing real software from other vendors.