The articles about Skype reading your BIOS have been making the rounds, such as this article here. Essentially, it looks like Skype goes out and reads the 64KB just below 1MB and saves it away into a file. This works because the Windows DOS box gives read-only access to the BIOS area. Apparently symptoms started showing up when folks starting running the Skype on 64-bit Vista, which doesn't allow DOS executables to run.
So what, exactly, is in that 64Kb which is so valuable? Good question. That portion of the BIOS is actually constructed out of a few pieces of the original flash device. Possibilities include:
1. The SMBIOS tables. These tables contain a series of records which describe various pieces of information about your system, much of which is not exposed in any other way. For example, it includes information about the type of DIMMs you have on your platform, the computer manufacturer, the model numbers, number of PCIe slots, etc. The format of the tables is described in the SMBIOS specification, produced and regularly updated by the Desktop Management Task Force (DMTF). See here for information on the release of the SMBIOS 2.5 specification last December, which added, among other things, new CPU types, new types of system enclosures for CompactPCI & AdvancedTCA, SATA/SAS port connector information, and an enum for fully-buffer DIMMs (FB-DIMMs).
2. The copyright notice. With a little bit of work, you can figure out the BIOS manufacturer and other tidbits from the various copyright strings.
3. Pointers to the ACPI tables.
Frankly, these are pretty poor pickings. All of this information is available through standard Windows interfaces, such as WMI. No magic here, considering someone went through a lot of trouble to save it away.
Update: Since the original post, Skype has commented publicly about it here, saying that it was used as a means of uniquely identifying the platform via their EasyBits framework. They state that the information was never sent back to Skype. According to this analysis here, the offending EasyBits were removed in version 3.0.0.216.
Tim
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