Espionage and sabotage are two things every government both loves and fears. Getting insight into potential enemies is critical and being able to slow them down without military involvement is a big plus. Having it happen to you, though, isn't so good.
Technology and the Internet make both of those incredibly easy these days. On the espionage side, several U.S. defense contractors have had data breaches where hackers stole valuable plans - including plans for the F-35 fighter from Lockheed.
On the sabotage side, the best example is the Stuxnet virus that crippled Iran's nuclear enrichment program for a while by sabotaging its centrifuges in subtle ways. Not only was it effective, it was impossible to say for sure what countries created the virus, although the U.S. and Israel are the logical choices.
Of course, that works both ways. I've warned you about the possibility for sabotage in public utilities like the U.S. power grid. And now thanks to 3-D printing, there's a new angle saboteurs can take.