This was back in Navajocoin (1.0) days and i did not have encrypted wallet. On Win7. I made some postings on this in this forum back when it happened. I lost coins from several different coins wallets.
Another Vote for 2FA Google or Authy. I already lost a number of coins NAV (1.0) included. Nuked my system and reinstalled from backup to stop it.
How you lost that? Trojan? Which system you used?