In terms of "shared resources", there is always a risk in someone inserting insecure codes or deleting secure codes (as Paul pointed out).
One method of alleviating these types of problems is using source control software and ensure that developers insert comments and give a complete history of the changes they've made. Nice thing of source control software, like Visual SourceSafe, is that you can restore to earlier versions of files in case one gets totally hosed.
Of course, this is only in the context of "shared resources", using source control systems for open source scripts and apps is not realistic.
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Buh Bye!
Cheers,
Me