I never lost access to the account. I'm still puzzled how this person was able to access my account and send a message to everyone on my friends list, given that I have Two-Factor Authentication on my account. Also, I'm supposed to receive an email whenever my account is accessed from an unknown device, which I did not receive. This sounds like somebody's been able to circumvent Steam's security?

Regardless, I've changed my passwords, including the password to my email account.

Account's compromised, don't click on anything it sends you - hope the owner can regain access.

this account is hacked. idk who this is anymore so im unfriending :(

Heads-up to anyone who's friends with LegendaryCerberus: his account's compromised. He may send you a message saying he's sent a $50 Steam gift card but the link leads to a misspelled domain that's presumably set up for phishing and harvesting login details. Don't enter your credentials on it.