No. In the strict sense, bug means an insect of the order Hemiptera (“true bugs”), and does not apply to other insects. read more
A worm/virus is a specific program designed to do some work (usually malicious). A bug is a behavior of part of a program that is not doing what it is supposed to do. read more
That depends on the worm. If you mean a caterpillar, then yes, that is considered a bug in larval form. read more