Fix malicious chinese characters being injected into php fil

As far as I can tell something has compromised our local machines - so it injects malicious chinese code into our php files. So I need two things. I need someone to clean the malicious code from about 21 php files and also help us solve the problem on our local machines. Code is not visible in notepad etc but is visible in something like firebug. It is also findable by file bloat. Fairly urgent fix required i.e. today. Dylan