FxCop organises its issues into five categories (the FxCop documentation refers to them as "Levels") of varying severity:
Individual issues can be suppressed by injecting a SuppressMessage attribute into the affected source file and defining CODE_ANALYSIS as a conditional compiler symbol.
See http://msdn.microsoft.com/en-us/library/bb429379.aspx for full details of the issues detected by FxCop.