Top-rated analyst Laura Martin of Needham downgraded Yahoo to hold from buy on Tuesday, citing a potential withdrawal of Verizon's $4.8 billion offer to buy the ailing internet giant.
"We worry that VZ will walk away or renegotiate its acquisition price lower owing to a 2014 hacking event that YHOO had not disclosed," Martin wrote in a research note.
Yahoo announced the 2014 the hacking last month.
Martin's picks have a 20 percent one-year average return with a 70 percent success rate, according to analyst ranking service TipRanks, placing her in the top 1 percent of all Wall Street analysts covering any industry.
Here's her investment thesis, and why she thinks Yahoo shares may have reached a ceiling.