Yahoo's humiliatingly huge data breaches could be used as leverage for Verizon, which plans to buy the online giant's Web properties, to get a significant discount on its planned $4.8 billion purchase, industry observers said Thursday.

Yahoo stock plunged 6 percent, closing at $38.41 per share on Thursday, a day after the company revealed that an unauthorized third party stole information from more than 1 billion user accounts in August 2013. That incident was separate from one that Yahoo had disclosed in September involving a breach of at least 500 million accounts in 2014.

If Verizon were to cite the recent data breaches as material events and back out of the deal, it could set a new legal precedent, said Ed McAndrew, a data security lawyer at the law firm of Ballard Spahr and a former federal prosecutor who dealt with cybercrimes. McAndrew said he doesn't know of any other cases involving a canceled acquisition that cited a data breach as the material event. "Verizon's decision-making may go a long way to helping define materiality, but they are in a bit of uncharted territory," McAndrew said.