When programs are created, though, they are generally compiled into machine language. Certainly programs in Pascal and C are. Some scripting languages use the source files, but Pascal and C don't qualify. The source code for PGP is available, and many people compile their program directly from the source, not trusting an already compiled version. More importantly, it doesn't matter how powerful your computer is, you can't decrypt a message with a key if you don't know the algorithm.
Key length is important, but so is the algorithm used.
Also, the importance of public-key encryption does not lie simply in the strength of the algorithm. Correspondents who have not met can be completely sure of the authentication of the other without ever knowing identities. Finally, there is my field, viruses. Viruses do not infect data or, if they do, they just corrupt it, rather than continuing to spread. And finally, what you have isn't a virus, and, no, it isn't a worm either.