What happened

Shares of software company BlackBerry Limited (BB 1.10%) are enjoying their third straight day of stock market gains -- indeed, their strongest gains of the streak -- Friday, up 9.9% in 12:45 p.m. EST trading.

You can probably thank Robinhood for that.

Glowing green line climbs on a stock screen.

Image source: Getty Images.

So what

In case you've missed the story -- been hibernating, perhaps? -- the past few weeks have been rather...exciting for investors in the kinds of heavily shorted stocks favored by traders on the Robinhood stock trading app, and actively on Reddit's WallStreetBets. The first four weeks of January saw BlackBerry stock more than quadruple in price as Robinhood traders worked in concert to "squeeze" investors who had shorted BlackBerry stock.

That rally came to an abrupt end last week, however, when Robinhood began restricting its customers' ability to buy shares of certain stocks -- BlackBerry among them. In a single trading day last Thursday, BlackBerry lost 42% of its market cap.

Now what

Robinhood's customers were not amused.

Responding to customer complaints, though, on Tuesday this week, Robinhood lifted trading restrictions from BlackBerry stock and, as of today, the broker confirms that "there are currently no temporary limits to increasing your positions" in any stock.  

Traders today seem to be taking that as a green light to resume buying, and resume squeezing the shorts -- and BlackBerry stock is off to the races once again.