Stock trading app Robinhood and Reddit group WallStreetBets have been making headlines this week after investors dramatically drove up the prices of GameStop, AMC and other individual stocks. But now some are questioning whether this is a stunt or a scam. 

After the meteoric rise of GameStop stock, from about $4 a share six months ago to $483 a share on Thursday morning, Robinhood and other trading platforms restricted trades on certain securities, including GameStop and AMC. 

Amid this week’s extraordinary circumstances in the market, we made a tough decision today to temporarily limit buying for certain securities. As a brokerage firm, we have many financial requirements,” Robinhood said in a statement. “These requirements exist to protect investors and the markets and we take our responsibilities to comply with them seriously, including through the measures we have taken today.”

With many retail investors (also known as non-professional individual investors) locked out for the moment, the trading frenzy around these stocks, particularly GameStop, is now being called a “pump and dump” scheme by both traders and outside experts.