Third-party websites claiming to offer COMSOL 3.5a for free are almost always distributing:
Version 3.5a was a significant release that introduced several modules and features still referenced in academic research: ResearchGate Comsol Multiphysics 3.5a Free Download
While there is no official "free" version of COMSOL Multiphysics 3.5a Third-party websites claiming to offer COMSOL 3