failedLoginCount=12455. Something's wrong ? MacOsX 10.14 (Mojave)

Question

Each time I reboot my Mac, i have a strange new (porn) image as background. I suspect i've been pirated. So i tried to have a look at users via bash command

dscl . -readall /Users > DSCLoutput.txt

and have this record :

dsAttrTypeNative:accountPolicyData:
 <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>creationTime</key>
    <real>1538548762.317136</real>
    <key>failedLoginCount</key>
    <integer>12455</integer>
    <key>failedLoginTimestamp</key>
    <real>1527346875.7267098</real>
</dict>
</plist>

Can I do something ? I changed my root passwd and reboot, but another image still appear.

Thank you

Answer 1

use KnockKnock to see what's running, post screenshot.