Ukrainian domestic election monitoring organizations and projects using crowdsourcing for mapping election violations (see GV post) reported [uk] being DDoS-ed on the day of the vote:

[...] web-sites of election monitoring organizations are experiencing DDos attacks. Maidan, OPORA, ElectUa.

Watcher.com.ua wrote [uk] that websites of opposition parties Frontzmin.ua [uk], Tymoshenko.ua [uk] and grytsenko.com.ua [uk] were also down due to a DDos attack.