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 mentioned 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 protect your Parallels account with two-step verification. Once two-step verification 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-step verification, follow the instructions in KB 125441.