Start with the OWASP top 10, in that order. By far most the most common problems are...well, the most common. :)
I also think that taking inventory of, and classifying the data that each system deals with is really important so you can prioritize your efforts.
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Start with the OWASP top 10, in that order. By far most the most common problems are...well, the most common. :)
I also think that taking inventory of, and classifying the data that each system deals with is really important so you can prioritize your efforts.