No need to reinvent the wheel, so here it is verbatim from the
Firebird 1 release notes (with due credit and © to Helen/IBPhoenix
and whoever else):

Windows ME and XP Windows ME and XP (Home and Professional editions)
there is a feature called System Restore, that causes auto-updating
(backup caching?) of all files on the system having a ".gdb" suffix.

The effect is to slow down InterBase/Firebird database access to a
virtual standstill as the files are backed up every time an I/O
operation occurs. (On XP there is no System Restore on the .NET
Servers). A file in the Windows directory of ME,
c:\windows\system\filelist.xml, contains "protected file
types". ".gdb" is named there. Charlie Caro originally recommended
deleting the GDB extension from the "includes" section of this file.
However, since then, it has been demonstrated that WinME might be
rebuilding this list. In XP, it is not possible to edit filelist.xml
at all.

On ME, the permanent workarounds suggested are one of:
use FDB
(Firebird DB) as the extension for your primary database files
move
the database to C:\My Documents, which is ignored by System Restore

switch off System Restore entirely (consult Windows doc for
instructions).

On Windows XP Home and Professional editions you can move your
databases to a separate partition and set System Restore to exclude
that volume. Windows XP uses smart copy, so the overhead seen in
Windows ME may be less of an issue on XP, for smaller files at least.
For larger files (e.g. Firebird database files, natch!) there doesn't
seem to be a better answer as long as you have ".gdb" files located
in the general filesystem.

This leaves the security database isc4.gdb, which is considered
writable by the code that should be simply validating a user's login,
in order that isc4's header be updated for that transaction.
Therefore, WinME probably makes a backup each time a user logs in. We
are trying to get an accurate problem description and a proven
workaround to publish here. If you can help with the description
and/or workaround, please post a message to the ib-support list or to
the firebird-devel newsgroup interface at news://news.atkin.com

Regards,
Andrew Ferguson
-- I think wrestling is real.