A new bill signed into law by California governor Jerry Brown will ban undeclared bots — automated online accounts designed to locate and disseminate information surrounding certain themes, keywords and people — during elections.

The new legislation is in response to reports that Russian-controlled bots overwhelmed Twitter during the 2016 United States presidential election, retweeting then-presidential candidate Donald Trump’s tweets 470,000 times while only retweeting Hillary Clinton’s tweets under 50,000 times, according to Twitter.

"This bill would, with certain exceptions, make it unlawful for any person to use a bot to communicate or interact with another person in California online with the intent to mislead the other person about its artificial identity for the purpose of knowingly deceiving the person about the content of the communication in order to incentivise a purchase or sale of goods or services in a commercial transaction or to influence a vote in an election," the bill reads.

However, experts caution that the new law might be tough to enforce.

"It's a very useful rule but it might become an arms race — can you catch them?" said Professor Ralph Schroeder from the Oxford Internet Institute.

"They will have to decide whether to pursue someone, and at that stage it becomes difficult because bots are difficult to trace.

"It also raises further questions about whether there are also positive bots and they get caught up in all this."

The new bill, which also targets bots designed for the purpose of selling items without being transparent about their identity, becomes law on July 1, 2019.