Attachments are stored "privately" in the data/pages/ directory (with paths like data/pages/<pagename>/attachments/<filename>) and can only be retrieved by using the AttachFile action (via URLs like http://example.org/mywiki/<SomePage>?action=AttachFile&do=get&target=filename.ext).
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The direct serving method (deprecated since long) was finally removed in moin 1.7.0. If you have used it until now (attachments = {...}), please copy your attachments into your data directory (and make sure they arrive at the right location there).