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There are multiple threads on the Gmail support forums, as well as a good deal of Twitter chatter, but so far no response from Google.
Every indication is that this appears to be a bug and not an exploit, as many people initially feared (so your Gmail account was likely not compromised, and no one is reading your emails). Speculation is that the bug is a result of a change in the way Gmail handles IMAP support. The issue is also reportedly affecting Gmail on Android and iPhone phones.