When trying log into Facebook, the message comes up: Your computer appears to be infected with a malwareI've tried different browsers, same result with all. Apparently the session thinks my computer is infected. How can the browser know that my computer is infected? I really did not know that it was infected. It's aMac. If that's the case it's only this user. Might be something else the browser is complaining about. I'm on OS X 10.6 with Firefox 8.Update: It turned out that Facebook has shut my accout down without notice, NOT telling me, right. The least they could do is sending me an email telling me but I guess they don't bother. The error message is pointless. 
Facebook. Why do I get the Your computer appears to be infected with a malware message?
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Firefox uses Phishing and Malware Protection, which is a Google service. Basically, it checks the sites that you visit against lists of reported phishing and malware sites. This link explains the technical details of the Safe Browsing protocol.Google has an support article on this notice as well.Why does Google think my computer is infected?Some forms of malicious software will alter your computer settings to redirect some or all of your traffic through a proxy controlled by the attacker. When you use Google, the proxy forwards your query to the real Google servers to fetch the search results. If our system detects that a search came through one of these proxies, we display the warning.