Is this error a hack attempt?

[Peter Knight]

Hi guys.

Just received an automated email from PW regarding an error on my guest account. I wondered what the message below meant. IE someone trying to login or run some API scripts or a hack attempt?

There is a guest account in my install but no one has been assigned to it.

Page: http://www.test-domain.com/http404/
User: guest

Error:
Exception: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '41-0' for key 'PRIMARY' (in /var/www/vhosts/test-domain.com/httpdocs/wire/core/FieldtypeMulti.php line 261)

#0 [internal function]: FieldtypeMulti->___savePageField(Object(User), Object(Field))
#1 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Wire.php(365): call_user_func_array(Array, Array)
#2 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Wire.php(320): Wire->runHooks('savePageField', Array)
#3 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Pages.php(1275): Wire->__call('savePageField', Array)
#4 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Pages.php(1275): FieldtypeNotifications->savePageField(Object(User), Object(Field))
#5 [internal function]: Pages->___saveField(Object(User), 'notifications', Array)
#6 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Wire.php(365): call_user_func_array(Array, Array)
#7 /var/www/vhosts/test-domain.com/httpdocs/wire/core/Wire.php(320): Wire->runHooks('saveField', Array)

[LostKobrakai]

The guest user is automatically assinged to every user of your page, who isn't logged in. So someone / something (bot, seo crawler) visited your 404 page and triggered the following exeption, which just says, there was somehow a duplicated entry in what seems like the notifications field. 

Edit: I don't know for how long, but some time ago processwire started to send emails to the admins if a site throws errors.

[Peter Knight]

Good to know. I saw Integrity constraint violation and Wire->runHooks('savePageField', Array) and assumed the worst.

[LostKobrakai]

You'll get a integrity constraint violation everytime you try to save stuff to the database with duplicated keys, e.g. duplicated page id's or other things which should only exist in a single row in the db. It's about the integrity of the database tables and uniqueness of keys, not about security. But your error still comes from a attempt to save something like this, so you should still have a look, what's causing the error.