First off your computer doesn't operate on IE5. IE5 is not an OS, it is a browser. If you think that downloading large files from fansub sites will get your information stolen etc etc... Then I suggest you just stop downloading stuff from the net all together.
And as far as your "large files can be disguised".... That is why you run a virus protection program, and you look at the file extension before you play or run things. Simply NOT downloading big files is not any kind of protection. Small files can be just as deadly is you are not smart about how you do things.