I have received a notification email from Parallels that my account was signed-in to from an unknown web browser, or mobile device, or location.
You received this email because someone accessed your Parallels account from the mention resource. This sign-in is possible when two-factor authentication for your Parallels account is disabled.
If you don’t identify the web browser or mobile device, operating system, IP address, location, date and time, then someone else accessed your Parallels account. This may happen if you’re using the same password in multiple services, including Parallels, and your password was compromised through 3-rd party services.
If you don't recognize the sign-in, change your account password immediately.
We also strongly recommend you to protect your Parallels account with two-factor authentication. Once two-factor authentication is enabled, Parallels sends you a notification email each time an attempt to sign-in to your Parallels account is made from a web browser or device that hasn't been approved before. In this case, an intruder cannot proceed to your account without your permission, even if they have the password. Each device or browser needs to be approved only once.
To enable two-factor authentication, follow the instructions in KB 124346.