Federation (and other) logs are, for the most part, susceptible to manipulation by computer experts. The principle is that if they're used as the basis for legal proceedings that they're treated as any other piece of evidence, normally highly reliable but potentially alterable.
GRAL: These accusations are absurd. We had nothing to do with this alleged attack.
ARCHER: The Andorian sensor logs. Look them over yourself.
GRAL: Logs can be fabricated.
ENT: Babel One
DAX: If you want, you can check our ship's logs and they'll prove it to you.
COLYUS: Logs can be tampered with. Well, you ought know that. After all, you claim to be a Security Officer.
Note that there are ways of cross-checking the logs with other logs to confirm their veracity
DATA: By comparing the Stargazer's main computer log with Captain Picard's personal log, I have found checksum discrepancies, sir.
RIKER: What does that mean?
DATA: All information is time-coded by entry, and the bits when totaled produce an aggregate amount which
TNG: The Battle
And later in DS9 we see that there are some kinds of logs (highly specialised, rarely used, extraordinarily expensive) that are basically unfakeable.
GARAK: When Senator Vreenak arrives, you will show him a holographic recording of a secret meeting held at the highest level of the Dominion in which the planned invasion of Romulus is being discussed. You will tell the Senator that this information was obtained through various covert means at great cost to the Federation. At least ten good men lost their lives bringing it across the line, that sort of thing. He will immediately suspect it's a forgery, but you will assure him that such a thing would be impossible. You see, Senator, this is an official Cardassian transcript. It was recorded on a one time optolythic data rod used for official record keeping. These rods are manufactured only as needed on Cardassia Prime. Information can only be transcribed on them once, and then cannot be altered.
SISKO: He'll want to examine it.
DS9: In the Pale Moonlight
Interestingly, the log in TOS: Court Martial is recognised as being susceptible to tampering but since the only ones who could tamper with it are Kirk (the accused), Spock (his loyal Number One and basically above suspicion) and the victim, the idea that it might be inaccurate was discounted out of hand until Spock noticed that the computer was acting funny.
COGLEY: Hypothetically, Mister Spock. Hypothetically, Miss Shaw. If what you suggest had been done, it would be beyond the capabilities
of most men. Is that true?
COGLEY: What man aboard ship would it not be beyond?
SPOCK: The Captain, myself, and the records officer.
TOS: Court Martial