Hacking government and hacking software are different things. You can't offer TCP/IP $100M to leak you some private keys from the server.
The smaller the government, the more value you could get per bribe (more power located in individuals) and the easier it would be to do it (smaller governments presumably lack layers of security measures against bribery). In case of extremely small government a big corporation could buy it out entirely.
In smaller government there is one and only one person you come to. If this person does not accept your bribe (or "lobbying") then you have to play by the rules.
In larger government there are a lot of competing bodies with vague job descriptions. You can honey them all with varying results. You can oil "layers of security" as well so those rarely help.
Don't confuse big/small government with big/small country. Surely there are banana republics, but I can't imagine you can buy out government of Iceland that easily.
The most minimal government possible is reduced to just the scary parts. That's the thing. A smaller government is no less scary in a police/military sense, unless you actually make the military and police smaller.
The irony is that everyone who goes on about a marginal tax increase, social security or some land-use regulations being tyranny, all of those same exact people are the biggest cheerleaders for a less restrained military.
You can downsize military as well. It's easier with smaller government because there is one person responsible, if they say we downsize military, we downsize it.
Compare it with having a dozen of committees with everyone in it being mediocre and fearing change, fearing initiative, fearing that something will happen after the downsize.
Committees are good at reacting (one loud incident -> wham you've got new regulations) and bad at acting (runaway project will run forever with nobody having balls to shut it down).
What makes you think so? Smaller government has smaller "attack surface", as hackers say.