"The uncomfortable reality of our world today is that bits and bytes can be as threatening as bullets and bombs, " Dempsey said in a letter Wednesday to Sen.

MSN: Senate may go on recess without passing cyber bill

The letter was drafted by Hans Bethe, who headed the group that designed the world's first nuclear bombs and who has served as a senior adviser to previous presidents on nuclear and anti-ballistic missile issues.

CNN: US - Critics blast U.S. anti-missile system on eve of key test

These weapons are designated with the letter "B" followed by the number of the physics package they contain, such as the B61 family of bombs.

CENTERFORSECURITYPOLICY: US Nuclear Stockpile