This is a classic argument against open source, but security through obscurity never works. If you want to keep safe from script kiddies, always keep your software up to date.
And with respect to the point cshimmin makes, there is some merit to it. Yes nearly every piece of software, open or closed source is bound to have vulnerabilities. However, the chance of someone taking the time for finding and exploiting a moderately hard to find bug (not referring to a run-of-the-mill sql injection) in a piece of software I've written myself and I'am the only user of is vastly lower than in case of a popular piece of open source forum software (to some extend depending on who I - the only user - am of course).
i'm not subscribing to the "enough eyeballs, all bugs are shallow"-argument, but the opposite is also wrong. deeply wrong.