'Last Activity' is frozen on a date for everyone
 

The last activity is frozen for every user on a date in the past, which is 10-03-2016.
How can I fix this?

Link please? What version of vB? What version of PHP? When exactly did the problem start and did you change anything on your vB site at that time or was something changed on your server at that time?

• The vBulletin version is 4.2.3
• PHP Version 5.4.45-0+deb7u2

The problem started from the date notified in my first post above. Our server got compromised by a hacker, but we will able to recover from it, luckilly. The site contains mature content since it's a dating site, so I don't think it's allowed for me to post the URL.

Are there some sort of tests I can execute, or files/settings I need to double check to fix this problem?

After getting hacked, did you reupload all new default files? Have you checked the server time? Is that March 10 or October 3 on your site? Did you restore from a backup database or just assume the database was fine? Have you checked the post.dateline fields and seen what is there and used a unixtime converter to see if that is the date in the database?