[Cryptography] Has formal verification actually been useful in the real world?

[James A. Donald]

Has a complete formally verified system been deployed anywhere?  Is 
there one keeping the electricity grid up?  Or a formally verified 
browser?  Or even software for converting graphics files to images on 
the screen so that a broken image will not take control of your computer?

Back in the days of usenet there used to be an old and obscure unix 
based usenet browser that would crash on unusual control character 
sequences and start executing usenet post text as machine code.  Is 
there any proof that that cannot happen with unusual html or graphics?