In a letter to Twitter Inc, which was included in the filing, Musk's advisers cited the whistleblower report by former executive Peiter Zatko — also known by his hacker handle "Mudge".
Zatko, who served as Twitter's head of security until he was fired this year, alleged in his complaint to US officials that the company misled regulators about its poor cybersecurity defences and its negligence in attempting to root out fake accounts that spread disinformation.
The Musk letter, addressed to Twitter's chief legal officer Vijaya Gadde, said Zatko's allegations provide extra reasons to end the deal if the July termination notice "is determined to be invalid for any reason".
Billionaire Musk has spent months alleging that the company he agreed to acquire undercounted its fake and spam accounts, which means he doesn't have to go through with the deal.
In a separate SEC filing, Twitter responded to what it called Musk's latest "purported termination", saying it's "based solely on statements made by a third party that, as Twitter has previously stated, are riddled with inconsistencies and inaccuracies and lack important context".
Zatko received a subpoena Saturday from Musk's team compelling him to testify in what Zatko's lawyers emphasised would be an "involuntary" deposition ahead of the coming courtroom battle between Twitter and Musk.
"He did not make his whistleblower disclosures to the appropriate governmental bodies to benefit Musk or to harm Twitter, but rather to protect the American public and Twitter shareholders," Zatko's lawyers wrote.
Twitter is likely to amend its lawsuit to include Zatko's allegations, so the court can decide on the bot and cybersecurity issues. That could delay the trial because Musk will say he needs more time to prepare, said Brian Quinn, a law professor at Boston College.
The court will have to decide whether the bot or cybersecurity issues are a "material adverse effect" that will harm Twitter's business for years — a difficult legal bar to clear, Quinn said.
The bot issue, which Twitter disclosed in filings with the SEC, seems to be an issue that Twitter would win on, Quinn said. Cybersecurity problems raised by Zatko may not be such an easy victory, he said.
"This is more grist for the mill," Quinn said. "It's not as obvious for the most part that this is a winner for Twitter. But once you start to analyse these closely, it's still an uphill battle for Musk."
