Apple (AAPL) is arguably one of the most successful companies of all time. With a market cap above $620 billion and annual revenues of more than $230 billion, the tech giant seems unstoppable.

But a short note by UBS analyst Steven Milunovich warns Apple should be on the lookout for three big threats.

Threat #1: An attack from below

“The most obvious [serious threat] is that Apple is attacked by ‘good enough’ phones, and customers no longer are willing to pay the Apple premium,” said Milunovich, though he added the bull argument that consumers are Apple’s main customers and they are willing to pay a premium for the brand.

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Threat #2: Messaging and bots

Products like the newly-announced Facebook (FB) Messenger Bot Store could take away from the Apple App Store’s estimated $50 billion in sales, according to Milunovich.

“Messaging could take on many of the roles apps provide,” Milunovich said. “In China, WeChat provides high functionality, such as paying bills, hailing a cab, and checking into flights through apps within apps.”

Threat #3: China could protect its smartphone market

Speaking of China, Milunovich notes the country is responsible for two-thirds of Apple’s growth. However, he points out the country has a history protecting its homegrown tech companies.

“A more serious issue would be if the government were to favor domestic suppliers as we have seen in enterprise computing,” he said. “IBM (IBM), HP (HPQ, HPE), and Cisco (CSCO) have suffered declining sales in China as domestic champions like Lenovo and Huawei mature.”

Nonetheless, Milunovich maintains a buy rating on Apple and has a $120 price target on the stock.

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