Your friend is just one of the person who is negative about in bitcoin. I don't know if he/she just discouraging you about it. But Nowadays you don't have to worry about it, due to bitcoin is continuously becoming more stronger and everyday there are more investor investing about the system of bitcoin has.
I don't know if your friend is negative about bitcoin. One thing for sure, your friend has an attitude of thinking that he knows it all, or somehow read some article and speculate or judge things without prior research. With bitcoin encryption system, and it's high level of security, i doubt you friend can hack it with just a calculator.