I have coins stored on wallets created with mymonero.com. Are they less secure than a paper wallet created with moneroaddress.org?
Unfortunately yes, fluffypony discourages storing any relatively large amounts there because webwallets always bring an additional layer of risk. Therefore, I would recommend to use https://moneroaddress.org to create a paper wallet. Alternatively, if you are fairly paranoid, use this guide:
https://www.reddit.com/r/Monero/comments/48cgmd/an_extensive_guide_for_securely_generating_an/
The guide ensures that the only way your coins can get stolen is physical access, which is extremely rare. It might take you a few hours to get familiar and comfortable with, but in the end it brings ease to the mind.
If I understood correctly (bear in mind that this rarely happens
) fluffypony was referring to the possibility of MITM attacks. So every time you access mymonero you are incurring the risk of getting your coins stolen. So, afaik, there is nothing less secure with the wallets created with mymonero (discounting the 13 vs 24 word mnemonic).If you, for whatever reason, used mymonero to create a coldish wallet, and never login again, you should be pretty safeish. And instead of logging in to transfer your funds to a proper cold address/account, you'd be better off not to. Wait instead for the short mnemonic seed to be supported by simplewallet.
Guys in the know: amirite?
EDIT: Adding context
https://www.reddit.com/r/Monero/comments/491gbj/i_lost_some_monero_that_i_had_on_mymonerocom/d0ocdpm