REUTERS/Darren StaplesWhen Cristiano Ronaldo attacks defenders on the soccer field, he does so with a quickness that leaves their heads spinning. Before they know it, they've lost. A controversial investment brokerage Ronaldo has been advertising on Twitter can sometimes have a similar effect on investors, according to a report from Donal Griffin of Bloomberg News. Offering products called contracts for difference, Exness Group allows investors to make highly leveraged trades that can provide outsized gains on the way up — but also can result in deep, swift losses in the event of a downturn. The firm, based in Cyprus, allows clients to borrow funds totaling up to 500 times their original deposits.