when mydoom first came out Astaro's defs had not yet been updated..therefore i have about 10 get through..i use mozilla so i had not issues..i simply have ASL now blocking 55 attachments tyupes(including exe and zip among others) so i do not have to worry about any possible delays in defs behing pushed out...btw my ASL is set to update hourly.
up2date hourly is the best what you can do, but you should also have a desktop antivirprogramm e.g. mcafee. read the actual ct-magazine to see the tests.
