In Harry Potter and the Order of the Phoenix (Ch. 22):
At once, Harry's scar burned white-hot, as though the old wound had burst open again - and unbidden, unwanted, but terrifyingly strong, there rose within Harry a hatred so powerful he felt, for that instant, he would like nothing better than to strike - to bite - to sink his fangs into the man before him.
This could mean 2 things:
- Either Harry was very angry and Lord Voldemort had successfully transferred his thoughts to kill Dumbledore for the moment. But given he wanted to sink his fangs, it is perhaps that Nagini did this.
- It might be a hyperbole that Harry was so angry with Dumbledore that he not only wanted to strike Dumbledore but give him a high degree of pain.
It seems like the first one has been considered as Dumbledore was careful enough not to be in direct contact with harry anytime. Only when Harry was in his office reporting Mr. Weasley's injuries, had this thought of harming Dumbledore happened. I don't know how Dumbledore noticed such a short though (Perhaps his skill in Legilimency?) but he did take notice and took extra precautions by asking Snape to teach Harry Occlumency.
This focus on the first point doesn't give any counter-proofs to the fact that Harry was a Horcrux and this might have affected him. As seen with the other Horcruxes, the person possessing the Horcrux has more affinity for darker thoughts. We sometimes see that Harry is overly moody and prone to rising temper. There are several incidents like what happened with Aunt Marge at 4PD or several times when he was at Hogwarts.
Is it mentioned somewhere how a living Horcrux affected the thoughts? Can somebody support or attack this statement with references.