From the original paper, "For example, SECDED (single error-correction, double error detection) can correct only a single-bit error within a 64-bit word. If a word contains two victims, however, SECDED cannot correct the resulting double-bit error. And for three or more victims, SECDED cannot even detect the multi-bit error,leading to silent data corruption. Therefore, we conclude that SECDED is not failsafe against disturbance errors."

The challenge for the attacker is to produce a 3 or more bit failure before a 2-bit failure occurs, which would trigger some alarms. I haven't seen any research on the feasibility of such an attack.

Additionally, there are stronger ECC schemes than SECDED, for example the one in IBM's ChipKill. It is hard to imagine a RowHammer attack that could remain undetected with such a scheme.

It is fair to say that ECC memory raises the bar for attackers.

Not to mention the schemes that treat RAM as untrusted with cryptographic, integrity checks. Those architectures are making more sense than ever now.

ECC may indeed help, but it wouldn't really fix the root of the problem: the fact that bit flips like this can happen at all.

google target row refresh, TRR