BlackBerry's New York-listed shares jumped about 20 cents shortly before 1 p.m. ET (1800 GMT), immediately after Citron Research tweeted a link to its report.

The stock briefly topped $9, but fell back, and was last up 3.5 percent for the day at $8.86.

Citron is run by California-based investor Andrew Luck, who is better known for short-selling stocks.

(Reporting by Alastair Sharp and Allison Martell; Editing by Jeffrey Hodgson and Chizu Nomiyama)