Curiously, if the second half of the user agent string is reversed and the number is removed, it reads "edit by joel backdoor," suggesting it was intentionally placed there.
The affected models likely include D-Link's DIR-100, DI-524, DI-524UP, DI-604S, DI-604UP, DI-604+, TM-G5240 and possibly the DIR-615. The same firmware is also used in the BRL-04UR and BRL-04CW routers
Personally, I would recommend a TP-Link Router (reff link) as a replacement. That's basically what I use.