Investing.com - With concerns about fraud already high, cryptocurrencies are facing another credibility problem: cyber attacks.Two new studies raise questions about the safety of initial coin offerings and their vulnerability to cyber criminals. More than 10% of the $3.7 billion raised through ICOs thus far was lost or stolen in attacks, according to Ernst and Young.Phishing was the most commonly used tactic by cyber criminals in the 372 ICOs studied.Another study found that online ICO platforms are attacked an average of 100 times a month by hackers. The study by Russia-based Group-IB also found phishing to be the biggest threat.Cyber criminals who once preyed on banks are now using the same tactics on cryptocurrency ICOs, which tend to underestimate the security risks.The number of hacker attempts has increased ten-fold since the beginning of 2017, according to Group-IB.