Cyber espionage was on the agenda in Beijing this week as Chinese Premier Li Keqiang met with U.S. Treasury Secretary Jack Lew.

Hacking also came up when Lew met China's new president Xi Jinping on Tuesday.

But how big is the threat? Why is China engaging in hack attacks directed at the US? And, as hacking is allegedly happening by both the US and China, how bad is it going to get?

For insight into U.S.-China cyberwarfare, I talked to Christopher Johnson, a senior adviser at the U.S.-based Center for Strategic and International Studies.

He points out that not all the attacks from China are state-sponsored, as there are so-called patriotic hackers and industrial cyber-spies at work as well.

As for any meaningful dialogue between the US and China to set up rules to regulate cyber-warfare, Johnson is optimistic.

"What we're looking for between the two sides in these negotations is a genaral set of rules on the road," he says.

"For example, things like critical infrastructure are red lines for both sides and therefore off the table."

So go ahead and try to hack into my network - just don't hack the hospital.