A rollback could not cause that unless you had a transaction open since November (and if you had, you'd have known by now due to the blocking and the tran log growth)
Sounds like something is logging in every couple of days and changing the values. Check jobs, make sure there's nothing odd. Otherwise maybe a server-side trace for logins and updates to that table.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability