Virii can infect any type of file. Extensions are meaningless except to Windows. however those same extensions tell windows whether or not to let the file be executable. Theoretically a virus could take over a JPEG, for instance, but you would have to set the extension to .exe or .pif to make it run, and if it doesn't run it doesn't do anything. On linux, the equivalent would be setting the user permission to 1, 3, or 7, on MacOS9, by setting the CRTR in the Resource Fork to APPL. There is another type of windows virus, called a Macrovirus, which takes advantage of security holes in Word/Office macros. You could make a Java class virus, but it wouldn't do anything because Java classes don't get access to anything except processor time. Anything else that executes code (reading an OBJect file or a PP2 or CR2, etc doesn't count as executing code even though it looks like code) could activate viral activity. The worst, though, infect the boot sector of the hard drive itself and execute instructions at the BIOS level, below Windows' control -- these can also infect other machines with the same basic architecture (ie, Intel/AMD boot sector virii can infect both Windows and Intel-built Linux boxes). but they still have to get there somehow -- something has to write them to the boot sector in the first place, which has to be executable in some way. One thing to watch out for though -- most plugins DO execute code. So that free filter for Photoshop or 3DSMax primitive generator you found, for instance, should definitely be scanned if you do not know and trust the source. And at this point this is actually vaguely on-topic because it's educational to Poser (and other) users and a virus infection can prevent Poser from working, after all -- and EvoShandor does not need to panic that a FreeStuff download would be a threat (malicious ZIP files are ones that do things like overwrite :Runtime:Libraries:ZygotePeople:Stephanie.cr2 with a blank file, and can be avoided by unzipping somewhere besides directly into the target folder and placing things manually) unless that FreeStuff download is an executable file. (And presumably, one you purchase on 'rosity has already been screened).