I received an email (via GMail) containing single URL link. For the purpose of this question, it is irrelevant whether link came from someone I know, because origin can be spoofed or faked.
More or less. GMail does a pretty good job filtering spoofed email addresses, as long as the corresponding domains have DKIM and/or SPF set up.
Of course, anybody with access to the email account (e.g., malware) can still send those mails, but that's different form header spoofing.
That means that if the link points to some malicious site, either your friend's email account has been compromised or you shouldn't call him a friend. In either case, contact him (preferably not via email).
How can I verify that the link points to some some virus/trojan/malware? It there software that helps me to verify this without endangering my PC?
A website can only infect your computer if it exploits some vulnerability in your web browser or – much likelier – one of its plug-ins.
In Google Chrome, e.g., you can set Plug-ins to Click to play in chrome://settings/content, so you have to give your permission explicitly to run a plug-in on a site.
As always, you should run periodic updates for your web browser, the OS itself and your malware scanner (assuming you use one).
Is using Chrome Incognito mode the right solution?
No. Incognito was designed to prevent leaving traces on your computer, not to protect it from malicious websites.
This is not satisfactory. Their intention might be to infect you, in which case they will answer in positive, and you get infected. – Andrei – 2013-02-08T17:42:12.063
1I was addressing the "it is irrelevant whether link came from someone I know, because origin can be spoofed or faked." point you made. Doing what I suggest is confirming origin, making "Who it came from" relevent. If you got a legitimate email from someone you don't trust and you wan't to know how to open it, that is a different issue. If that is your real question you should re-word your original question to reflect that and I will delete this answer as it does not apply to that question. – Scott Chamberlain – 2013-02-08T17:45:42.153
Even someone you known can have intention to infect your computer, not even speaking about someone you do not know. Assuming here that sender's identity is not faked. – Andrei – 2013-02-08T17:48:58.213
If that is the case, if the sender is a person *you can trust* not to send you a infected link, *and* you have verified the real identity of the sender, *and* they confirmed they sent you the link, *and* they can attest that the link is not infected, *and* you trust their judgement on the fact that the link is not infected.... Then you can open the link. Other than that, I just say never open them. – Scott Chamberlain – 2013-02-08T17:53:48.393
You move the answer from technical area to subjective/psychological. That fails. (1) Unsuspecting user can forward infected link, unknowingly. (2) You assume I am supposed to know precisely level of trust of everybody who sends me emails. I think this is naive assumption. In short, I prefer technical solution, not psychologival/subjective. – Andrei – 2013-02-12T19:14:56.860