1. A method for preventing undesirable behavior by an executable code module received from a potentially untrusted source, comprising: (i) querying a database for identifying information corresponding to an executable code module received at a host system; (ii) when step (i) returns a predetermined result, scanning the code module for an indication that the code module has a potential to cause undesired behavior in the receiving host when executed; and (iii) when step (ii) finds the indication the code module has the potential to cause undesired behavior in the receiving host when executed, preventing execution of the code module at the receiving host.